Some of the most fascinating automotive stories simply come from the intricacies of running a massive multi-national corporation like General Motors. Rules, policies, engineering edicts, and other guidelines ensured uniformity and a strict adherence to the Alfred Sloan hierarchy, but creative folks could always find a workaround. But sometimes, GM did it to itself, creating something, then hiding it from the public. The L88 427 Corvette was such a situation, where Chevy hid it in plain sight by giving it an artificially low horsepower rating and a huge price tag to coax buyers into buying a more street-friendly and affordable L71 427/435 instead. But sometimes—sometimes—they just built something then forgot to tell anyone about it at all, and that’s the case with this 1969 Chevrolet Impala SS427 convertible.

If you wanted an Impala SS in 1969, a 427 was the only engine choice. The standard engine was the L36 which made 390 horsepower with a hydraulic cam and pretty friendly street manners, ideal for a big luxury car like this. A lesser-known option was the LS1, which made a relatively tame 335 horsepower. But for reasons that aren’t altogether clear, there was a third 427—the legendary L72 425 horsepower version—that GM decided the public didn’t need to know about. No advertising promotions, no mention of this motor in any of the promotional and sales materials, and unless you were sharp with the order form, you probably didn’t even know you could get such a thing in 1969, because Chevy certainly wasn’t talking about it. A total of 546 L72 engines were built and they were installed in a variety of Chevy vehicles (they were not exclusive to the Impala, you could get it in your Kingswood station wagon if you were savvy), making them quite rare. Mission accomplished, Chevrolet!

This incredible 1969 Impala SS427 convertible is a real-deal L72 car, purchased new by John Cornstubble (no, I’m not making this up) of El Dorado Springs, Missouri on May 12, 1969. The number of L72 Impala SS427 convertibles built can probably be counted on one hand, making them some of the rarest and most highly-sought of Chevy’s heavy cruisers. Even more significantly, this one is fully documented, with original purchase documents, Protect-O-Plate, and receipts from nearly five decades of life. It still carries its original, numbers-matching L72 427/425 engine and was recently treated to a cost-no-object restoration by the pros at Boot Hill Automotive Resurrection in Toronto, Ontario. We have photographs documenting, well, just about everything as well as significant ownership history and photos of the car in-period. This car has one heck of a pedigree no matter how you look at it.

Here are the relevant details:

Protect-O-Plate:

164679S (037146) Production #
1: Chevrolet Motor Division
64: Impala 8 cylinder
67: Convertible
9: 1969
T0907LS
T: Tonawanda
0907: September 7 build date
LS: TH400 for Impala SS 427/425 Hi-Perf L72
69Y275: Build date of the TH400 transmission, October 1st of 1968 (275th day of 1969)

DK1015G

DK: Posi-Traction 3:55 Large Ring
G: Detroit Gear and Axle
1015: October 15, 1968
1: Power steering
1: Power brakes
3: AM radio
3: Front disc brakes

Cowl Tag:

69: Model year 1969
1: Chevrolet Motor Division
64: Impala 8 cylinder
67: Convertible
STL: St. Louis assembly plant
138170: Sequence number
858: Parchment vinyl bench seat
65: Olympic Gold
B: Black vinyl convertible top
10C: Third week of October build date

In person, the restoration is simply spectacular. Olympic Gold is this car’s original color and it works rather well on the full-sized ragtop, offering just the right combination of flash and elegance. The car appears to have been extremely solid prior to the restoration and as far as we can tell, it’s still wearing all its original sheetmetal, including floors and quarter panels. The big doors open and close so easily and precisely that your first few slams are a little too hard, and the hood latches with just your fingertips. The two-stage urethane paint has a fantastic shine complements of some of the best guys in the business, and it has been color-sanded and buffed to a fantastic shine. All of the correct emblems are in place, and yes, for those of you wondering, that stick-on deck lid ‘SS’ is how the factory did it. The bumpers have been refinished, the stainless is polished, and if there’s any demerit on the car, one of the wheel arch moldings has a few minor dings in it, as it is surely original. But there just aren’t many nits to pick on this gorgeous car.

The cowl tag says this car original carried a Parchment interior, but when it was restored it was treated to a correct black interior instead, and the contrast is striking. Obviously, as a color change, everything in the car was replaced with a brand new piece, including the seat covers, door panels, side panels, and all the little detail pieces in between. The dash pad is excellent and the carpets are brand new, replicating the original weave. The upscale Impala also received some warm-looking faux wood accents that perfectly match the woodgrained steering wheel, which sits on an optional tilt steering column, a rather rare option, SS or not. This car also carries factory power windows, which is a very desirable feature in a big luxury car like this, and the wide bench seats mean there’s plenty of room for everyone when you go cruising. The gauges show bright, crisp markings and we strongly suspect that the 43,500 or so miles shown on the odometer is correct, as it was not rolled back during the restoration. The only notable deviation from stock is a later digital AM/FM/cassette stereo radio in the dash, but the original pushbutton AM radio is included with the sale of the car if you’d like to take it back to 100% stock condition. The top is brand new black vinyl with a correct glass rear window, and it powers itself up and down easily, latching at the header without a struggle. It fits beautifully and we suspect that our photo session was the first time it’s ever been down.

The good stuff is all under the hood, however. The L72 is the real deal, with a fantastic big camshaft idle and a torque curve that feels like it could pull forever. While someone with true performance intentions might have purchased a Chevelle or even a Camaro in 1969, lucky Mr. Cornstubble got a full-sized luxury car that hits several classes below its weight class, because this car is surprisingly fast. The engine was fully rebuilt to stock specs and still carries its original cylinder heads and correct aluminum “Winters” intake with a big Holley 4-barrel up top. It starts easily and while it’s a big grumpy when it’s cold, it is nevertheless content to idle all day and sits in traffic without getting cranky. The engine bay is detailed for show, with Chevy Orange paint on the block itself and proper fasteners and hardware throughout. There are some who say that the L72 should have an open-element air cleaner, but it appears that this air cleaner has been on the car from a very early age, perhaps even when it was new, and the original chrome valve covers were replaced with painted valve covers simply because the owner liked the low-key look better (the original chrome valve covers are included with the car). An Optima battery provides the juice and makes the big, high-compression V8 spin over easily, although it’s not 100% authentic, of course.

Underneath, the TH400 3-speed automatic transmission was rebuilt and bolted to the back of the 427 and linked to a heavy-duty 12-bolt rear end with 3.55 gears and a Posi limited slip unit inside. Much of the suspension features upgraded Hotchkis components, including a pair of seriously beefy sway bars, because the intention was to build an L72 that would be a blast to drive. You’ll also find a beautifully crafted stainless steel exhaust system with welds that should be on display in a museum; it’s just beautifully done. The floors, frame, and suspension components are in exemplary condition with correct hardware used throughout, so it wouldn’t take much to put this car into 100% original, show-worthy shape, but it would truly be a shame to take it off the road. Simple color-matched steel wheels with “dog dish” hubcaps were how this car came from the factory, so they were cleaned, painted, and fitted with fat 235/75/15 Coker redline radials for a period-perfect look.

Documentation is pretty extensive. There’s the original Protect-O-Plate and service booklet, manuals, and an album full of restoration photos, all of which will accompany the car. This is quite likely the finest of its kind anywhere, and with a strong pedigree and equally strong performance, this awesome Imp makes for the best kind of hobby car.