C= 2WD, K= 4WD. The title and the Vin plate need to match. The vin plate needs to show original attachment, never removed. Then there is the frame stamp. That stamp may just have the numbers and not the C/K. At any rate, the truck is not a NAPCO. There are no 1/2 T Napco's after 1959. The are not called Napcos. They are factory 4X4's. (K10)(K14)(K15)
Before 1960 there are Dealer Napcos, DIY Napco's, upfitter Napco's and factory Napco's. All legit if built with the kit, on or around the time period. Lots of so-called Napcos built from donor parts, etc. Some under the name "restored". It was pretty easy because all the trucks had the same chassis with leaf spings. Then when independent front suspension/rear coil came along there had to be two different chassis. C and K, etc. This truck is one of those mysteries that has to be investigated to get the true story. You may see where the independent front suspension was removed and leaf springs added. The rear trailing arms, and etc., would be converted to leaf. It could have been built any number of ways. It also depends on the components and other tell tale features. The factory 4x4 in 60-66 used the same basic drivetrain as the former Napco's (divorced transfer case/3 drive shafts). All kinds of VIN swaps, frame swaps, chassis swaps, illegal swaps and legit DIY swaps have been done. K designation started in 1960.
Most likely this truck is a clone, a latter day conversion.
Frank50, I do not see any 4WD chassis pics in your links.