Interesting, I thought that may have been the case. Huh, go figure, I had seen from so many sources the 15x8's included in the WS6 were supposed to have larger tyres. I believe RPO QCY tyres were included in WS6, and conveniently, that looks like what the '78 Formula was optioned with on the dealer invoice, so now I know I just need to get four sets of the same tyre.
Shame most retailers down here don't stock 225/70/r15 BFGoodriches! I was hoping to get a bulk deal