prepping drivetrain for the new engine- 8.75 & 904, need advice

i want to build the trans myself. i can find a core, and i have a friend who has done 904s and 727s for a looong time, would rather not spend all that money on buying a pre-finished one. and i know it's possible to fit 325s back there with a minitub. it's gonna be tight, but it'll work. thanks gd though, i'm gonna give them a call.