My '71 ain't a '71...or is it?
Just for your Mopar knowledge bank: Slant 6 904s and 318 904s aren't interchangeable. Different bolt pattern and plenty of smallblocks came with 904s.
Extra credit: a lotta people such as myself actually keep the 904 even with a high performance build because they can be built to handle plenty of horsepower (650+) and rob significantly less power than a 727.