Thats what I was thinking, Sub.. when I saw that F54XA I ran it thru the cruncher.. thinking perhaps whatever agency originally titled the vehicle used a combination of both the engine number and the vehicle serial number.
F54XA came up in the VIN Cruncher as a 1954 made in January, of unknown type, wheelbase, or plant, but that's just because the 54 is in the right "year spot" in that sequence of numbers.
ZB54PU at first looked like it would be usable, again, because the 54 in the "year spot", but it looks like '53 thru 55 first series Serials would have had to start with one of the following letters followed by the '54':
H,J,K,L,M,N,P,R,S,T,U,V,W,X,Y or Z
In order to be a "pickup" (which IMO would be a 1/2 ton or 3/4 ton) that first letter in a 53 thru 55 1st series would have to be an H, J or K
A 'Z' as the first character would indicate a 2 ton truck.
If you take the 'B' out of ZB54PU you come up with a 2 ton utility with a 212" Wheelbase made in Pontiac, MI of unknown month.
