big bolt pattern backing plates

SGBARRACUDA said
Not true, I had a 1980 Mirada with a 7 1/4. I put a 68 B-body housing under it and used the 7 1/4 brakes, drums, backing plates. No problem

Mirada is a, I believe, 'J' body. It has the same 5 bolt pattern as all BUT 'A' body 7-1/4.

A body 7-1/4s use a 4 bolt pattern to retain the axles.

Mark.