Caliper problem

I upgraded my 68 B'cuda to 73 Duster disc brakes. I came across a really good deal on some reman calipers supposedly for a 78 Cordoba. Everything fit together with no problem, until now. I was mounting a set of 14" Magnum 500's and the caliper outside corners hit the rim. Any body know if there is a difference in the a-body calipers that would allow for this rim?