Yeah, but it is an easy job. I've done it several times. The B body axle is NOT a good fit for any Valiant or Dart EXCEPT for the Demon or Dart Sport. The low hanging wheel opening arches make for a real tight fit.
I bet it would, I love swapping a B Body into an E Body for the extra room but I’ve used all of my B Body axles in my E Bodies!!! Never thought about sticking one in a Duster/Demon/Sport!
Of course you don’t need to move pads on the B to E swap.