You should talk to CRT or A&A Trans; but for reference, my old 904 went several seasons as a basically stock unit with only good clutches & bands, a deep pan and a RMVB. 4400 stall, 3000lb footbrake drag car. Pay attention to the converter hub welded area, had a problem there after getting to 600HP & 5800 stall. That was probably age-related.
At about 640HP, 6000 stall & low 10s, the stock parts were beyond their limits; I stepped up to a CRT 904 and it's been great.