You don't need to go all crazy for a 904 to handle the power you are going to be putting through it. Just remember that. People get all caught up in all these exotic parts etc when it is not necessary. If you want the low gear set that is your choice. I have a a999 that is tore down in my shop right now that has the Low gear set but it only had 4 clutches in the front drum. So take that for what it is worth.
The 904 that I built I copied and used the parts that were recommended to me from guys I know that have been successful racing. The parts I was told to use will easily handle more than most would ever put through it. From how hard they run their cars I do not doubt them for 1 bit. Cost of parts was somewhere in the $500.00 range not counting the Valve body or Converter. This was the first one I have ever built and I probably got maybe 6 Hours total into it from tear down to painted…. Done.
What you will find out is when you go to get the parts, no single vendor will have them all. I would also say stay away from the BIG name brand guys because they will for sure take all your $$ for the exact same thing you can get down the street for a lot less. There is no magic to building one of these transmissions but most will try and brain wash you & will try to get you to believe different.
Also there is no need to find a certain year transmission for the 5 clutch front pak. Use the thin Reds and steels to make your own 5 Clutch front Drum. This is what I did. Simple easy.
This should be plenty of info on where to get the parts and at least get you started.
Pump Gears** $36
http://www.tcsproducts.com/products/product/13/
24 Spring* $105
http://www.tcsproducts.com/products/product/15/
Billet Strut* $19
http://www.tcsproducts.com/products/product/618/
Rear Kevlar Band* $18
http://www.oregonperformancetransmi...OD&Category_Code=904&Product_Code=PTB-12820AK
Kevlar front Band $19
http://www.oregonperformancetransmi...D&Category_Code=904&Product_Code=PTB-12905F-K
Servo** $17
http://www.oregonperformancetransmi...ROD&Category_Code=904&Product_Code=SNX-22912A
Makco 904 page.* thin clutches/steels & Kits
http://www.makcotransmissionparts.com/A904.html
WIT trans, teflon seals, trans exploded view
https://www.wittrans.com/search.aspx?SearchTerm=12175ct
https://www.wittrans.com/Schematic.aspx?Transmission=A904
Valve body of your choice and Lever to match.
http://tranzactofindy.com/index.html
Converter…. Call a good vendor and have it custom made for your application.
Lenny at Ultimate has xlnt customer service and does great work.
http://www.ultimateconverter.com