The engine number indicates it was built in Flint Michigan, the numbers indicate the date built (11=November, 13 day of the month), and L indicates it was originally built for a 6000 series truck. There really isn't a serial number for the engine just the date code, so all engines built on the same day would have the same numbers.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.