tranmission???
For any serious big block I'd use a 727. You can build a 904 to handle the power but it becomes real expensive real fast and with big block torque you won't see any appreciable gain running a 904. If your racing a heads up class and need that every last .01 the 904 is the way to go but again it'll cost ya. There are several good places to get parts. Andrews Racing
http://www.andrewsracingtrans.com/Transmissions/727/index.html and Cope Racing Trans.
http://www.coperacingtrans.com/ are members here on the board and are very knowledgeable and stand up guys. Rick Allison at A&A Transmission
http://www.aandatrans.com/ is also very knowledgeable and honest.