The sender reducer/adapter that Brad refers to works in later 235/261 heads that were made for an electrical sender that had a wider diameter than the mechanical/tube sender (sometime after 55-1st).
Presumably, you are referring to a 1940 216 head and 1941 216/235 head? Maybe that hole changed when the 235 was introduced?
That reducer might work in an earlier 216/235?
It was available at NAPA - I'll look for the part number.
