Need help identifying a VIN

[LuckyLightning]

Hi guys,

I'm looking to purchase a '79 K20. The seller sent me a pic of the vehicle certification sticker/tag. I'm using the LMC catalog VIN decoder but I'm hitting some snags: there are some numbers where letters should be.

Here's what I have:

Ck12391xxxxxx

C = Chevrolet
k = 4x4
1 = (this should either be an "L" for the 350, but it looks like a "1")
2 = 3/4 ton
3 = (this should be a "4" because it's a pick-up)
9 = 1979
1 = (there are no assembly plant options that even look like a "1")

Also, lower on the service sticker is stated "Service Body" underneath the "() Truck" option, but for "() MPV" it just has "XX" and in the parenthesis brackets and I have no idea what that means.

I went to carfax and it just says I entered an incorrect VIN.

I've had a few '60-'66 trucks but this would be my first square body. I appreciate any and all help.

Thanks for looking.