Will a reaar end, springs and driveshaft from a 70 Dart 2dr fit in a 66 2dr?

Good catch on the torque converter nose/crankshaft counterbore mismatch.

A '66 Dart and a '70 Dart both have a 111" wheelbase, and with a 7-1/4" rear axle and 904 trans there'll be the smaller 7260 U-joints in both cars, so that's not a concern.