Does this transmission have a little lever to pull up to get it in reverse? If so it is probably the original and has straight-cut (spur) gears and is not synchronized. Most drivers double-clutch this box to shift. If it has no lever and reverse is left and down it is probably a SM-420 swapped from a 48-53? truck with torque tube drive. Lots of parts are still available for them. Look
here for good info. The 1950 trans will be a SM-420. Good Luck
