Since the clutches are smaller in the 904 there is less clutch area to absorb the torque. More clutches help as does more line pressure but some of the billet drums for the 904 offer a larger apply piston so there is more area on the apply so more clamp force for the same given pressure. I guess what I'm saying is although there may be little to no chance of the drum exploding due to a sprag failure like the 727, then the additional piston area may be a good reason to consider the aftermarket drum for the 904.