1966 Plymouth Valiant Shift Linkage Help

Sounds silly, but have you lubricated the linkage and checked the fluid level in the transmission? Also, after all these years- there is going to be a bit of play. Too much and shifting is tough.
Also, check clutch adjustment - if the input shaft is still spinning it can cause shifting issues. Many parts to consider especially with column shifted cars. Very cool set up and Welcome aboard!
Syleng1