Mustang & Fords magazine has recently done some flow tests of 351C 2v and 4v heads vs. aftermarket 351W aluminum heads. According to them, the new technology 351W heads out perform the factory Cleveland heads, and are bolt on. So, it may be a good idea to at least explore all options before going to the trouble of converting 351C heads to fit on a 351W.

Good luck.

-Jim