I'm not sure exactly when the naming convention was changed, but I'll
answer as best I can.
Earlier models (up till 1987) used the C and K designations for 2wd and
4wd as you stated. They also used 10, 20, and 30 to represent 1/2,
3/4, and 1 ton vehicles.
Later it was changed to R and V for 2wd and 4wd respectively, and the
weight capacity was listed as 1500, 2500, and 3500 for 1/2, 3/4, and 1
So your 1984 4x4 truck (provided that it's a half ton) would be a K10.
If it were a 1989 model for example, it should be a V1500. Same thing,
different naming scheme.
This document pertains to Blazers, but should help explain some of