In my application, an adapter had to be used (with the other/first switch I listed). I found a brass T that allowed connection to the oil-pressure-source, the oil pressure gauge, and the pressure switch (for current to the chokes).

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.