Working on a conversion from auto to manual 4-speed on my '67 Firebird. Confused as all get out with the original Hurst/Saginaw linkage set I needed. Exploring everything I can read out there from every source.
Found this info on a Camaro site. Lots of applicable info and pictures to figure out shifters, linkages, and Saginaw/Muncie background facts that (sometimes) crosses over to the Firebird. I know it's Camaro, but there is referenced uses in the articles on Firebirds.
The shifter info with linkage pics for linkage arms helped me out of a jam. Perhaps it will help others out too with their First Gen Birds. If not directly applicable, it's at least an interesting read with lots of facts from the era.