If you are looking for power do NOT waste money on 302 heads....the ports are tiny, don't flow much, and are not good for power focused builds. They do work fine on stock, low HP builds (like for trucks, daily drivers and such).
For what its worth, I did a head comparo years ago between some home ported 302's and some home ported J's on my old 318. Long story short, the J's were over half a second faster at the drag strip on that little 318. If you are interested in making power, spend your money on a good after market head (Edelbrock, Trick Flow, Etc).