maybe for parts but not for a restoration.
I can think of a couple of things that are different right off the bat without looking at mine. The AC lines go through the firewall on an E-body in little round holes but the B-body has a rectangle fitting. Also the top of the cowl holes are shaped differently . I'm talking about '71 to '74 B's compared to E's.
On the parts that rusts out around the brake booster and under the windshield wiper motor look very similar and may even be the same besides extra holes for wiring and such on B's. below that the floorboards and tranny tunnel are similar but not the same
I always thought you could make a convincing looking 'CUDA or Challenger with the front half of a '71 B-body welded to the back half of a E.
The doors are located a little differently but the E fenders bolt right up on the top of the shear panels but the bottom dog legs are a little short. Even on the '73 and '74 B-bods with the iso suspension
Maybe you could make a good race car from parts of both instead of cutting up a perfectly good E-body,, Kind of a Monster Garage solution I guess