Actually, you're expecting a lot out of 350 inches. Your parts look good but to get 425 HP from 350ci means you'll have to spin it harder. 224 degrees will run out @ about 5500 rpm's. If those are the RHS 200's, they will support more rpm's and be able to take advantage of more cam. Just be realistic about your intended usage of the vehicle and the idle quality. I would get a stroker crank(they're cheap nowadays). 425 HP from 383ci is much easier without needing so many rpm's.