Make it live by bolstering the top end, Need to really put a goal and a budget together before you can answer this question. I have personally ran a twin 900+ hp boat on stock spiral bevel geared uppers with IMCO bottoms. Did it break every now and then It would tear up the small bearings in the top between the gears. But Most don't beleive it.
Anyhow if your not chaning the gears to XR or even if you are, Have Max Machine Worx install their big tower in the case, and use their billet 2" top cap, with 7/16" studs. This along with the solid pinion shimming kit will keep your upper gears aligned properly under higher hp, and that's the big key, they also have a suggested concoction of oil that we have used with decent results, but Merc HP gearlube works great as well. Even if you choose not to get the tower installed, at least stick their top cap on and do the pinion shims. You said its a single Fountain is it turning a Left handed Wheel?? they often do, and if it does it is driving on the gear that is against the top cap, very important, to get some rigidity in there and not let the gears deflect from one another.
