Using a 66 A-100 8 3/4 in a Early A body

The rear is usable it just needs narrowed a bit, it can go to stock A body width or 2" narrower than stock depending on which axles it has, some have 3" of taper and some have 4" of taper.

If you're on a budget its a great piece to start with, if you're swapping in everything new then it's nothing special. Back 12-15 years ago one of my friends was running resplined A100 axles in his 451 Dart, 11.60's on motor 10.90's on a powershot plate which is advertised 125hp, never hurt the rear but blew up 2 converters with it.