You would be miles ahead by repairing the three on the tree than to try to adapt a floor shifter to the 3 speed. There are many rod ends, a bell crank, and bushings which wear out, but can be either repaired or replaced. There is an adjustment which needs to be done to the shift box.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission