how much horsepower can a 904 handle?

If I was gonna build one for say 400 or so HP, I would would want high capacity drums that will hold more clutches, like a five clutch forward drum. If you go on WIT Transmissions they have all that stuff. I would want 4 pinion planetaries........I've heard Bighead440 say the aluminum ones are fine, although some argue the steel ones, Bighead owns a transmission shop so he oughtta know. Maybe we can get his opinion.

@Bighead440