What pressure should the fuel pressure sensing switch be rated at for a 1955 235 series 2 engine?
If you mean "oil pressure sensing switch", most of the combination fuel pump and idiot light switches operate at 7 PSI of OIL PRESSURE. That prevents the pump from continuing to run if the engine stalls, or in case of a rollover. Fuel pump pressure on a carbureted engine needs to be 5 PSI or less, sometimes a lot less if you're using some sort of Mickey Mouse aftermarket carb like one of the Weber types.
Jerry