ddlong - First off Welcome to Stovebolt!

I added a little detail to your title so folks can get a better idea of what you're asking.

On that note, a check of the GM Heritage site provides this
1949 Chevrolet Truck Data PDF which provides the answer to your question and a whole lot of other info on the truck once you read through it.
Your VIN (technically a vehicle serial number as standardized VIN's did come along until much later) decodes as:
3 = St. Louis (Assembly Plant where built)
GS = 1949 Chevrolet 3800 1 Ton truck (code for model year and series number)
A = January (month of production)
1381 = 381st Chevrolet Truck built at the St. Louis Plant that year (Sequential Unit Number which started with 1001 as the 1st truck built on the line)
The hydraulic bed and sides would have been specialty equipment not originally installed at the factory when built.
Looking forward to seeing and hearing more about your truck!
