Stock 904 how much hp can it handle

Until it breaks! LMAO It all depends on the internals of the transmission & how hard you are going to hammer it. Personally, I would use an aftermarket driveshaft. I know I do in my bracket car with 408 stroker, 904, rmvb, trans brake, & 5,000 dynamic converter on 29.5 x 10.5 slicks. SWAG on the 408 is 5-550 hp, I did crack the snout on one converter & dynamic made good on it.