OK, then the best donor truck for the harness would be a 1993-1994 C1500 automatic. A K1500 harness would do in a pinch with some minor re-work. Stick to 1993-1994 and 1500 though.
Earlier years won't have the electronic trans so that whole portion of the harness will be wrong. Also TPS connector is different 1990 and earlier, as well as a few other things, and pre-1991 the bulkhead pass-through on the passenger side is even shaped different so it won't fit without hacking.
Later years (1995 only actually) is such a drastic departure from earlier although still TBI. 1996-up totally useless as those are Vortec; practically no similarities at all.
Some of the major generations of TBI harnesses - not meant to be a concise guide, just rule of thumb:
1988-1990 non-electronic transmission, square-shaped passenger bulkhead pass-through, large 3-pin flat row TPS connector, AIR pump connector (may not be present in 1990), some early years may have port EGR (large finned EGR solenoid setup)
1991-1992 non-electronic transmission, rectangular-shaped passenger bulkhead pass-through, small 3-pin round TPS connector
1993-1994 electronic transmission, rectangular-shaped passenger bulkhead pass-through, 1994 will have purge valve solenoid connector
1995 one-year-only good luck etc. transmission adds PWM to TCC, 4WAL standard on pickups, driver side airbag (1500 and 2500LD), etc. and more of a Vortec-era inspired harness layout under the hood with electrical convenience center near brake booster
Of course each one has potential for differences depending on engine and emissions packages, GVWR, and the transmission choice - especially 4L60E vs. 4L80E or the more obvious manual vs. automatic
Y'all don't kill me for any errors or omissions; as I frequently say these days, it's been years since I've been hands-on with these trucks on a daily basis like I used to be. Like Kelly Bundy, each new thing I learn displaces something old.
Richard