Just to follow up a little, I'm not sure about the valve size on 2V heads, but on 4V heads it's 2.19 intake, 1.71 exhaust. You can sneeze on a 4V motor and get 400hp out of it without touching the heads (stock 10.6:1 CR or close depending on year). If you want to know more about clevelands, go to
www.mustangsandmore.com and post in the ford racing forum. There are a ton of classic guys that know a lot about the motors. I can also give you the AIM screen name of someone that put a 351C in an 86 if you want. The swap is NOT a problem.
------------------
Neal
69 stang
351C/4sp