Oooook, well, it makes a little more sense now. I saw the title of the thread and thought you were actually building something....you know....Fast (scream'n)....like a 10 second 318 that spins up in the stratosphere. Then I saw that you were looking at stock iron heads and the word "fast" went right out the window, lol. Still, sounds like you will have a spunky little 318 that makes good steam.
Considering your budget, I think you would get a lot more bang for the buck with a solid flat tappet cam (vs an expensive roller) and put your $$$ into something else (better heads maybe). Best of luck with the build.