I did my own wiring harness on the LS swap into my 76 K10
but if I had it to do over again I would just buy one or ship it off and have it done
You gotta ship off the computer and have it re programmed
If you want to do the harness yourself there are several sores with good instructions
And I would not bother removing the unused wires , just cut em off after you’re sure you don’t need em
I did my 73 bronco that way when I transplanted a efi mustang engine cause I was in a hurry , didn’t have any other vehicles to drive , I got all the parts together and did the swap over a long weekend
Also the NV-3500 five speed is a nice trans for street driving if you want another gear in the middle