904 Parts
I get most of my rebuild parts from
www.bulkpart.com and shop around for the best deal on any high perf parts I need at Cope Racing, A&A, etc. Something else you might need are specific select snap rings to get the clutch plate clearances set and you can find them at
www.wittrans.com There are numerous good converter builders. I'm running a PTC and it works great and didn't break the bank.
There really is no specific manual for a 904 except the factory serv manual or the ATSG manual which is nothing more than a copy of the factory serv. manual but Karl Munroe has a good manual out for the 727 which is very similar and it contains a lot of information on theory and operation and high perf. mods. Here's a link to it on Amazon
[ame="http://www.amazon.com/Torqueflite-A-727-Transmission-Handbook-HP1399/dp/B00E84G4BI/ref=sr_1_fkmr2_3?ie=UTF8&qid=1396231141&sr=8-3-fkmr2&keywords=karl+munroe+727"]Torqueflite A-727 Transmission Handbook HP1399: How to Rebuild or Modify Chrysler's A-727 Torqueflite for All Applications [Paperback] [2003] (Author) Carl Munroe: Amazon.com: Books[/ame]
The YouTube video's Rodzilla recommended are a great way to actually see things done. Gives you an idea on tools needed also.