The guys at A-1 Racing Transmissions told me years ago they could build me a 904 that would handle just about any small block combination I could put in front of it.
My ex-employer ran a B Altered Automatic race car. Power from Steve Schmidt(500 cu. in Chev) about 1200HP. Transmission 904. Best et, 6.9, speed, over 200MPH. Once held the NHRA record for his class. And yes the transmission held up.
The company he owned, developed many and manufactures many transmission parts for the racing/performance industry. His race car was the test mule for the products they make.