101 & 001 shells are the same. I've seen the swap done. You just pop off both halves of the body and replace the guts. I've seen in person a modded NES model with the nicer screen of the 101 so I know it works. Some for some reason think it won't since the button is on off on one and not the other but the internal housing is the same fit just a differing function to the button is all.

As for the NES GBA Nintendo released only 250K of the unit and it was notably before the 101 popped up.