youll find that one harness the issue. the different yhears, and cab configuration substantially change it. get both year manuals. do not get the haynes or chiltons. it has to be gm factorry service manual. it will tell you the different configurations. not trying to nitpick you, just saying its not as cut and dry as you think. some of the early year stuff had power and ground leads going to the passenger side firewall connector that later years did not. it literally changes all of the wiring. it looks subtle on the surface, but its not, it changes the cross chassis harness, and a lot of little things. and if one vehicle was c60/c59 and the other was c68 with auxillary you just opened a huge can of worms. trust me on this. get both manuals and study them before you start cutting wires brother. id hate to see you turn the donor harness into scrap by being overzealous.