['68OrangeSunshine]

Your engine number won't be related to the VIN. Truck engines did not get the body VIN stamped on them because with a truck, the engine was considered a replaceable item.
On L6 blocks, an ''engine dress number'' was stamped on a machined pad behind the distributor shaft hole. You can deduce the plant, build date, and original application frome these numbers and letters.
Example: F0626UH = Flint MI, June 26th, 292 w/manual xmsn -- 67-68.
Decoding lists are online or even in the LMC catalog.

I guess it was 20 years ago I had a 1967 cab tank cleaned out to replace my original '68 tank. The newer gasoline formulation was dissolving 30 years' worth of gunk from the bottom, clogging the carb -- and the twist-lock of the neck was chewed up from having lost the key to a locking gas cap. I guess you can't get it done anymore.