What exactly is wrong with the shifter?
The problems I've had with my '69 over the last 21 years is that the shift lever itself is loose where it mounts in the column (the pin hole wears) and the slider to the bottom is sluggish.
The sluggish/sticky slide is easy enough to fix, though a bit labor intensive. Pull the column out, dissasemble it and grease the sliding collars. Sometimes you can just squirt some spray oil on the lower slide while in the truck and loosen it (easier to have a friend working the shifter while doing so, but I did it myself).
Loose shifter handle - no good solution yet. I replaced the collar with another, but it's worn as well (the pin keeps working out). At one time I saw a kit that replaced the pin with a self-retaining assembly, but haven't seen it in the last 5 years or so... right now I have a flat machine screw loosely double nutted. Not Pretty, but at least the pin no longer falls out with me holding the detached lever in my hand.
I've thought about brazing up the hole in the collar to build it back up, but haven't done so yet.