1966 273 Commando - Thoughts

My son grenaded the 7 1/4 in his 72 Swinger. He replaced it with an 8.8" rear from an Explorer. It's a factory 318 car. Why would they put such a lame rear-ended in any V8 car?
You must drive it harder than Grandma did. Yep, the 7 1/4 rears can't take a lot of abuse. The 8.8 seems to be a good one. Rear disc?