Your '78 mounts are wrong for a Fox body. Get a set of '79-up mounts and it all fits. I put an '82 351 Windsor in my '79 'Tang and it bolted right in. The 7.5 rear stood up to 60K miles of abuse and never faltered. Only trouble I had was buckling the body, a set of homebuilt subframe connectors fixed that. And a shock tower/firewall brace, so the hood didn't pop up on a 1-2 powershift. Those bodies aren't all that tough, but that's why they go, they're light.