Too much horsepower?

I would be A LOT more worried about the car than the block and rear end at that level. The block should be fine as long as the machining is good and everything is well balanced. The rear end could end up being a problem, but, without SERIOUS mods, I would be most worried about twisting the body! 790hp is WAY beyond what a unibody car can take with out going into pretzel mode.