FMM - A quick scan through the
GM Heritage Vehicle Info Kits ID's that engine serial number to most likely be from 1960-62 Chevy C10, C20 or C30 (base 235 engine for each model):
F = Flint manufacturing plant
01 = Indicates the month of build (January)
12 = Indicates the day of the month of build (12th)
J = Base engine for C/K10-20 and C30 (per the 1961 chart)
Could have very easily been dropped into an early truck with only a few mods and transfer of earlier parts like flywheel, clutch, pressure plate, starter etc.
Look for a block casting date code just above the starter and post that. Decoding that info will give a better clue about what year.
