It appears to be a US chassis which uses an entirely different rear end though.
And for the record, my 66 Strato Chief 283 has a factory 12 bolt, so did my 66 Grande Parisienne 283 powerglide. I've seen a lot of 12 bolts in small block Canadian Pontiac B bodies, way more than the Chevy equivalent. I'm not sure why.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
The 26657 is the style or body number for an American Grand Prix. Canadian pontiacs have a 7 in front of the number like on your cowl tag 76657. The U.S. cars start with a 2 For pontiac 1 for chevy etc. The vin number will be on the frame I think rear passenger side on top Of frame.
