On YouTube, I have watched a lot of videos on our squarebodys. One is from 1AAuto and another guy milkcrate82. They both have numerous videos on how to do just about anything on the 73-87 Chevy Trucks.
https://www.youtube.com/user/1aauto/...cks+door+latch
https://www.youtube.com/user/milkcra...uck+door+latch