I have a lot of images saved of CP 427's, but can't say I have a 425 horse.

This must have been a very time limited option.

Yes, that info is thanks to Kevin's persistence as well as investment with GM Vintage Vehicle Services. There's been lots of stories of other 66 Parisiennes, Laurentians and Strato Chiefs with an L72 but no solid proof has ever surfaced, at least on Canadian Poncho.

Limited time option? You had 365 days potentially, spanning September '65 to summer '66 build-out to get your car built. Probably June was the cut-off for orders.

The big blocks were coming in from Tonawanda, so logistics were no different for any version. Given the very low installation rate that 427s had in these cars, my guess is that they just didn't justify taking responsibility for, parts wise for 10 years, for such a fringe combo. At Chrysler the Hemis were U.S.-built cars whereas Cornet / Satellite were built only to 383 in Canada, so too with Big Fords where in '65 the 390 was tops in Canada but 427 in the U.S.

Around 2006 I corresponded with an owner of a 1-of-6 1969 full-size Chevrolet with L72 power sold new in Canada. It was a U.S. built Impala Sport Coupe with a bench seat, M21, fender skirts & wheel covers originally. Sold new to a teacher in Windsor. I wonder what dealer, maybe Central Chev-Olds in London? They were up on the secret high-performance offerings.

I always admired Marv's stock looking dual quad 425HP 409 Corvair. I know its not a Pontiac but it just popped into my head for some reason, it is a stock drivetrain except for the 409 and a radiator.

Google Corvair with a 409, I think there is still a full build on the HAMB site.

I would like to see the 409 425hp and the 427 425hp both put on a dyno

What about a 2005/6 Pontiac GTO with LS2? They were 300kW (400hp) DIN rated. In SAE Gross terms that is well over 425hp SAE Gross.

Chevrolet learned the limits of the 409 & experimented with the Mark II Mystery Motor. They finally released it for production with the Mark IV. Done in 6.5 & 7 litre displacements for racing purposes (396 & 427) they brought power to the masses cheaply.

I say Chevrolet but come on, we were speaking of the lighter Chevrolet-based chassis Pontiacs and how cool and rare in such configuration they were. Canadians were a cheap lot and almost always bought the smaller engines for economy in it's many forms. In terms of purchase price, operating costs, insurance, and even license retention. And lets not forget cold-weather starting.

I always get a little excited when I see a barge of a Pontiac with big cubes and/or a 4-speed.

As a kid in the sixties there were Canadian Pontiacs everywhere. On my 20-house street there were 9. In many cases the badging was so discreet that you'd never know if that Parisienne down the street  might have a 427. Certainly that '66 Beaumont Sport Deluxe driving along the main road with dual exhaust & wheelcovers off might be hiding something.

Marv also did a Corvair 327 , I think it was a convertible. I met him at a Halifax car show a long time ago, he has a 63 BelAir 2 door post, dark blue, tan cloth, dog dish, 4 speed, air, and a 396 2 barrel. It had 409 markings on it, he said he put the 396 in it for good gas mileage. It was a 69 iirc. It also had those period correct tow tabs under the front bumper. He has a large 409 collection in his garage, a wall of valve covers, intakes, manifolds, heads, and blocks. Ive seen pictures of it on line.