No Chevy truck had an actual "VIN" number until 1954 the first year the feds required actual vin numbers.
The states either used the door post number or the engine number
The one Matt 50 gave decodes the body serial number while this page decodes the engine block serial number.
http://chevy.oldcarmanualproject.com/models/engine.htm
It should be noted that the engine serial number on AD trucks never matches the body serial number There are no "numbers matching" AD trucks. the feds didn't start requiring vin or partial vin on the engine blocks until 1968.
From a Chevelle page:
Beginning January 1, 1968 the federal government requested voluntary compliance of identifying major parts of a motor vehicle by inscribing or affixing an identifying number or symbol on major parts. As far as research has shown, Chevrolet did comply. by stamping a partial VIN on all engine blocks(1). Again, the location on the block may vary between the plants and years but one change was made in 1968. The GM division number ('1' for Chevrolet) was added to the partial VIN. A 1968 version of an Atlanta partial VIN stamping would 18A174373.