Hi Roger,
I'm new here but I'm also fiddling with my trans (50 Dodge wayfarer).
I have discovered that the shift linkage is unlike all others I have worked on.
Looking into the trans I see why.
The forks move on two rails , one on top of the other.
The shift lever on the top of trans moves the gear selector.
The bottom lever moves the selector up and down .
Down is 2nd/3rd. Up is 1st/reverse. I don't know which position the bottom lever should be in to select which rail yet.
If the gear selector will not move, move the bottom lever around moving the gear selector at the same time.
If the gear selector will not move at all, I would think that the trans is dry.
You would have to drain it , remove the cover and see if the sliders will move into gear.
You could jack up the rear end and spin the driveshaft to see what happens.
I doing this exact job today.
Good luck.
W