You would need to find a fairly special smith to do that job, but as far as function goes, I can't see any reason why it wouldn't work. Even older BAR'S without an adjustable gas block can be easily modified to be adjustable, and the case shapes are very close.
Many will question, "WHY?". It makes no sense economically, but what really does about this sort of stuff?
Guys invest 5 g's in an outfit that pokes holes in paper. Hmmm. Makes perfect financial sense to me!
A custom barreled 9.3 BAR? Cool!