You most likely figured this out:
F55MB F = Flint, MI engine plant
55 = 1955 1st series
MB = 235 truck engine in a 1 ton truck with automatic (Hydra-Matic) transmission
Since this is a truck engine, it most likely did not come from the factory with the 261 cam (as was used in the Corvette 235 version of that block).
