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

I have 10 3/4 x 1 3/4 drums on my 7 1/4 small bolt rear, might buy a 8 3/4 but no brakes. (few offers an choices to deal with).

1. will my backing plate fit on the 8 3/4?
2. if not will my guts of the brakes fit on an 8 3/4 backing plate.

brakes are new an would hate to lose out. I have been told that the flared drum shouldnt be on this car, 72 dodge dart swinger 318, 904 police fleet car that they came with different style drums, but the whole car is stock?

thanks
steve