V6 in a 1/2 ton?

[68C15]

this morning I got to looking at my 67 stepside VIN plate. granted this thing has been messed with more than a 65 year old prostitute but what I found interesting is its starts with CM15.
I wonder what kind of gear it may actually have. its a low hump floor with no shifter holes. I got excited when I saw 4.10 posi listed in the glovebox.........until I saw the vin there didnt match the plate.
as a matter of fact I'm not even sure this thing was originally a stepside, a short fleet or what.