3 Speed Shifter Problems

[Plumbers GMC]

My 1970 GMC 1500 1/2 Ton pick-up has suddenly developed a major problem with the 3 speed column shifter. The whole cone that supports the shift lever went all afloat at an intersection when I went to shift it into 1st gear . The lever would not make contact with the shift tube that surrounds the steering shaft. I took out the shift lever and found that it was OK and if I leave out the pin that holds the lever to the cone and push the lever in all the way I can still shift the truck.
Does anyone have any advice ? Is there a simple fix ? Mechanics have told me to take the column out and maybe it could be fixed.
Thanks,
Bob Bosworth
Fairhaven, MA.
PS I've had a long history with both GMC and Chevy trucks all of them had 4 speeds. This is the first 3 speed I've ever had.