Original equipment Canadian 15# rad cap??

[2qwik2c]

Anybody know if this 15# rad cap is a original equipment piece or a service replacement part?? I have seen this cap on a few cars in junk yards ( most cars in the yards were missing the rads) and also my 67 Impala convert has this rad cap, my 67 convert has not been messed with much and has been parked since 74 or so. So I'm thinking this cap may be a assembly line installed piece for Canadian built cars??
http://i141.photobucket.com/albums/r73/2qwik2c/cap3.jpg

[2qwik2c]

Compared to AC RC 15 cap.
http://i141.photobucket.com/albums/r73/2qwik2c/cap1.jpg

[luzl78]

the assembly line caps always seem to me to have a hollow center rivet as opposed to nos ones which are even across.