Ford changed the production method on these head's in the late 80's as a cost reduction. Any early 80's head's will work fine. If you were doing a complete rebuild I would suggest using 429's the held up much better. The pre-1980 head's were smaller chamber and used a dish piston.
FORD LETTERING CODE:
In the 1990's Ford decided to go with the international coding method and are nearly impossible to decode.
In the early version you can see the simplicity thus: C6 transmission production build 1966, E40D transmission production build 1984. That is not to say it was only used in that year, but it was the first year in production.
When in doubt :DON'T
Valley Station, Kentucky
Dream EXPression Racing