The original sending unit threads directly into threads cut into the cast iron of a 216 head. There is no bushing.
If a newer 235 engine is used in an AD truck, a brass adapter bushing is needed for the AD sending unit because the later 235 heads have a larger hole than what is in a 216 head.
This larger hole in the later 235 is there to accommodate an electric sending unit which is larger than a 216 sending unit.
I doubt if one would have much luck finding an electric sending unit small enough to fit in the smaller hole in a 216 head.
