Just be aware that if you end up going whole-hog on these (big valves, full machining) you'll be dangerously close to what a set ov new aluminum heads cost. Thats without even paying for porting. Pay for porting and you'll be over. I'd say if you already own the bigger valves, then do it, and port 'em enough to blend them in nicely. Make sure you machine the guide bosses for a higher lift cam, and something i would personally do, is machine the tops where the VC bolts up... they are always way off and the covers always leak.
If you dont own the valves already though, the costs to buy them and use them can add up quickly. By the time my (nice) core 915's left the shop, with (used) 'new' 2.14/1.81" valves, guides, seats, machining, a .030" shave, and cleaning and assembly i was out $900, including the price ov the cores. I wouldn't have bothered had i known, i would have saved another $300 and bought some aluminum.
And i agree vehemently with the above... you NEED zero-deck flat tops with closed chamber heads. Quench is good!
