Picked Up A 70' Dart Swinger

The wife and I went out and bought us a 70' Dart (for $500 from the original owner), for my 426 Max wedge engine which I am going to be installing. Can anyone advise me on an 8 3/4 rear end that will work for the Dart I just picked up. I am assuming the 7 1/4 rear that's in it will not hold up. I am also thinking of having a mini tub installed.

any advice?