That truck had Chevrolet clearly written in the grill just like both my '46 trucks.
The number on the plate was definately 5BK..
5 = Kansas City, MO
BK = Used on '42 thru '45 1/2 ton trucks)
The 4th character could have been an I, and L, or a 1
If civilian car and truck production was terminated on 2 Feb 1942, then I don't know what to think.. unless it was a "non civilian" truck.. but it said Chevrolet in the painted grill.. but I guess it might not have been the original to the truck grill.
I = September
L = December
Or it could have been two 1's.