Are the heads for 65-66 401 interchangeable they have different part numbers as well as the intake manifold(carter).
Heads for '65 and '66 401 and 425 are the same. They used valve seals (intake only) in '66. Some '66 425s had a Quadrajet. Hope this helps, Buford.
They are interchangeable but you may notice that the 1966 heads have SMOG ports in them. I noticed it the other day when I looked under the hood of a riviera and it had one 65 and one 66 head. The ports were noticeable but the two heads worked fine together. Ralph Nicastro Jr. 64 Skylark 401 nailhead Norwalk, CA