Yeah, that water pump will put you right up there at 400HP, no prob.(sorry but I couldn't resist)
It's really not as easy to make 400 horses out of a 350 as all the magazines and parts suppliers would like you to believe. But then again, all it takes is money(quite a bit of it actually).
I'm no help on the clutch other than to suggest that you buy a new one and don't go rebuilt. I never had any luck with the rebuilt ones.