I know Canadian built Pontiacs sourced a lot of their interiors from US fullsize Pontiacs....and some Chevrolets.....but I don't recall seeing the 66 GP upholstery elsewhere.....
Unique to 66 Grande Parisienne and not possible to make identical duplicates just by stitching. The pleats are done with heat so they actually have a bit of a "U" shape to each pleat, not just a flat stitch. Of course someone like SMS or the like with the ability to make dies could make it 100% authentic.
The December feature car has identical to original upholstery, other than that minor detail. All the spacing etc is 100% as an original, with all measurements taken from Ken's yellow 66 original upholstery before he got it redone.
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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
This is what I found on the 'net....for 66 2 plus 2....
The middle picture is obviously a 65 as evidenced by the gauges. The other two are 66 and as you can see the pattern is not the same as what is in the December feature car.
I am guessing the seat frames are the same but the upholstery is not.
One comment about the back seat in the feature car, the armrest is not correct for a Canadian car. I pulled that from a Bonneville and had it reupholstered for the 66 because I thought it suited the car very well with the Strato Bench front seat.
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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