That '55 and up balancer would have a 3/8" groove.

Presumably, you have a 12v generator, with a 3/8" groove?

JC's short-shaft pump for use on later 235/261 engines installed in earlier trucks has a 3/8" groove.

A good match for the correct diameter 3/8" belt.

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.