Buying used heads?

I have 2 sets of ported 516's, 1 set from Dwayne Porter, who's pretty well known. I spoke to him about the 516's and although they can be made to work, he said it takes just about twice as long to get them to flow a comparable number to a newer style casting, and you really need to know where to work, and NOT to work. Without a flow bench, I'm not sure you would be able to tell what you had. Aerohead sells factory castings with 2.14/1.81" valves for $500/pair. I'm sure they have the bare minimum done to them, but I would consider them a safer bet than most backyard sets. Good luck.