According to Fatman Fabrications, the '64 - 77 Chevelle and the '73 - '76 Torino have a 62" distance across wheel mount surface. The '67 - 69 Camaro, '68 - 79 Nova and '71 - 73 Mustang/Cougar have a 60" distance.
IMHO, you can't build anything too strong. Asking a GM 10 bolt or even a 12 bolt to take 400 hp is asking a lot.
