Unilug?

Hey, I'm looking for a little input on the (uni-lug?) type rim. This is the ones with oblong lug nut hole. I tracked down a set of Cragars with rubber for my 75 Caprice Classic vert. I think they will fit my Cutless also. Just wondering if I should be wary of these rims, naturally the guy selling said "no problem". They were on a GTO, the guy was not sure if they are a Chev/Ford or Chev/Mopar, any thoughts on that? Would like to try them on the 'cuda. Thanks in advance.
Spark.