New member who needs help with VIN

[x041040x]

Hello, been lurking for some time and enjoying all the great trucks here. I recently acquired a POS 1968 c10 with a work bed on it. I plan on making this my first project and I have ZERO experience so expect lots of questions and pleas for help.

First, of many, question. Please help me decode my VIN. I believe I have most taken care of but I'm thrown with one digit.

CS138Z156686

I have...
C = 2wd
S = 6 cyl
1 = 1/2 Ton
3 = ????? Maybe just cab no bed?????
Z = Fremont


What is the 3 mean, Also have no SPID Sticker.
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