The change happened in 1977, with the introduction of the /7's. I have never heard of one being called a bonehead ... however the earlier ones were called 'peanut' valve covers by some.
The /7 valve covers are supposed to be a bit stronger than the peanut covers. The covers are interchangable ... they have the same mounts and mounting surfaces.
The peanut covers do look a bit more retro, eh?