Yes it will bolt right in place.You might have to shorten your driveshaft though.Back when I first put the V8 and 8 3/4 in my 66 Dart,I used a driveshaft from a 73 Dart V8 car.I,ve since gone with a Dana 60 and chrome moly driveshaft.
I think that 8 1/4 rear is gonna have the big bolt pattern 5 on 4 1/2" axles, not a big deal just will need different rims, your 66 has 5 on 4" small pattern.