Mike (Urbansuburban) might have more info. for you Brian.
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Prince Edward Island
'64 Parisienne CS "barn find" - last on the road in '86 ... Owner Protection Plan booklet, original paint, original near-mint aqua interior, original aqua GM floor mats, original 283, factory posi, and original rust.
I seem to recall that the 64 bumper USA and Canadian bumper for wagon rear only, had the same bracket hole spacing. We were originally going to order a new one from the states but decided to have our straightened and re-chromed for half the price. I am thinking the Canadian and US had specific brackets to make the bumpers interchange.
The 64 wagon had a specific rear bumper as it has the extra holes by the reverse lights for the steps. also it does not have a curve in the center. I am not certain on the 63's but would bet that they are all pretty much the same as they were so close.
check out this link. he has some brackets. I have also contacted them in the past and found items not yest listed on their site. He supplied me some chrome for cost of shipping only that came off a wrecked car. We were able to get them straightened and are now on our car.
Ill bet its the shape of the inner fender compared to the right side. Mine was exactly the same. I had to cut and weld mine as it had a hole and was too thin in a spot.