As you start gathering your information about going to larger valves in the heads, remember too that you will probably have to do something about the small ports. Also, you'll want to know whether or not the valve guides are worn excessively, how much valve spring and at what installed height you'll need for the cam you choose, the surface of the head itself, equalizing the chamber volume, and a host of other things. Before dumping a lot of money into a set of heads that you're probably not going to be happy with their level of performance you might want to check around locally and on Craigslist, Racing Junk, eBay, etc for either a new or used set of aluminum heads that already have bigger valves and ports.... Just another consideration! Being a budget build, the time you spend doing research and a realistic cost comparison will probably save you money in the end...