71 Dodge Dart 273 swap to 318

once you have the 727 installed you have two options
measure the distance from the tranny to the rear end and have your stock unit shortened and rebalanced or measure it and have one made to spec
there are several list floating around with what size driveshafts people have and there are just too many variables to have one made before the motor and tranny are in

not everyone agree on the strength (or weakness) of the 7.25 rear end but most of us will agree it will hold up to the power of a 318

I wouldn't bother messing with it unless it broke