Nice project.
Just a casual observation.
Either your transmission is not an OD, OR you have the 3-4 shift lever on the wrong way. It should be upside down compared to the rest. That's how Chrysler made the OD. They flipped 3 and 4 around using the original high gear for third and OD becoming 4th. This is why the 3-4 lever needs to be upside down (pointing down) compared to the rest. In the one picture you posted of the linkage, it is facing up, which either means it is a standard 4 speed, or the lever is on upside down.