Happy to help. Here is the correct VIN decoder for your 1970 GMC. The F is for the Flint assembly plant.
KE203-FZ64735
K = 4wd
E = V-8
2= 3/4Ton
03 = Cab & Chassis
- = Space reserved for special Designation
F = Flint Assembly plant
Z = 1970
64735 = unique serial number, starts at 50001 in 1970
And here is the correct model number decoder for your truck. As you can see, the 03 designates it as a cab and chassis.
KE25903
K = 4wd
E = V-8
2 = 3/4Ton
59 = 127' Wheelbase
03 = Cab & Chassis