I build the 904 for a customers mid 10 second 3200 lb Dart (among other similar cars) and the most exotic part in them is billet servos. I use billet servos and good friction parts, but the drums and 2.74/1.55 planetary sets are bone stock - including the fiber thrust washers. A good valve body is a MUST to put big power through a 904 (I like the A&A reverse/LBA, although a T/A Cheetah works well, too), but it's the same for a 727. The billet servos are needed because of the increased apply pressure to the bands. The converter drive issue is as simple as having your converter made with an A500 pump drive, and using an A500 pump gear. I do kind of cherry pick the cores, using the H/D case (easy to spot with the tailshaft extension housing retainer plate on top). If I'm bored I lighten the sun shell. It gets freshened about every 3-4 years (500+/- passes) with about $100 of new friction parts, but we have never broke a hard part - (can you say exploded 727 clutch drum?). So I can't fathom why you need a $5000+ trans - or a 727, for that matter.