Take the 904 apart and see what broke. There are good aftermarket parts available for them. A "good" 727 uses 904 internal components. The advantage of a small block is you don't have to spend the money to get it all in a 727 case.

Small block car I would (1st) stick with the 904, (2nd) Glide with a gear set, (last resort) 727.

If the results don't match the theory, change the theory.