I agree with both Bartamos and Tiny.

You MPG low low.

What RPM or speed, and what type driving (steady speed or start-and-stop)?

steady-speed driving, I get:
16-18 mpg 45-55 mph
12-14 mpg 55-65 mph

3.55 rear ends
1954 235 & 1960 261 truck engines

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.