Would I have to alter this rear?

I scored an 8 3/4 off of craigslist today, going to pick it up next week. Guy says it came out of a late 60's roadrunner. says backing plate to backing plate is 51" or 51.5" (can't remember which) and it's got 2.98 suregrip. Not bad for $200... but my question to you knowledgeable folks... What will I have to do to install it? Just want to be prepared for what will happen. -Thanks!