The number cruncher on this site doesn't cover GMCs. Your number should be something like 101 P S1234. 101 means 1/2-ton short bed, P means Pontiac assy. plant, S means '58 or '59, the numbers are the production sequence. Lower numbers would be '58 production. Not sure when the change was. A '57 would have a T.
If your single headlights are in '59 fenders, it might be a
fleet option truck .
Check out
Old GMC trucks.com
