Calling all 1971 collectors...

I need a little help here. As most of you know, I live in Calgary. That's Canada. Which means O Pee Chee, not Topps. So I have a lot of these....
with these types of backs....

not these....

I have around 350 of these 1971 OPC cards... who in the heck can I trade with to try and get the rest??????

Also, why are all the backs like the Nolan Ryan above... except for one, which looks a lot like the Topps Palmer

If anyone has info on these, I'd love to hear it.... and if anyone knows a Canadian with a box of these in their attic, I'd like that info as well...