7 1/4 drums fit on 8 3/4?

That is the same brake setup that was on the 8 3/4 in the 72 demon parts car I bought.
I think it should swap straight across. I think the key will be to make sure your axles have the correct offset for that size brake.
I swapped all the 10 x 2 1/2 brake parts off my 73 large bolt 7 1/4 onto the 8 3/4 and I just had to make sure the large bolt axles I bought had the correct offset.
The backing plates, retaining pins, and the top bar of the e-brake hardware have to match the drums.