Its been a little while.......

You would have to e-mail lunati and see if they have a .904 Mopar grind one size smaller than that 10230701 for the SBM (as with others they used to use "universal" for short voodoos but said all of them are now Mopar specific- but check
284 is a long way from 256 you would need low gears, loose converter and have a race only motor, no low end
jones only has a few .904 hyd lobes , more soild his 256 is a great one