what he said above. They do offer more power, but you sacrifice Money (plenty of it) and time. You have to get adjustable valve train (usually roller rockers instead of adjustable pushrods) to adjust valve lash, and you have to keep adjusting it. Youll be able to hear it when it needs adjustment, but its best to do it before you hear it.
the deal above for the 430 head SHIPPED to you for $80 is a smikin' deal - I'll bet the shipping alone is half of that. since money is an issue right now, bolt it on and GO !