Hi, I'm Chris Wright. I am restoring a '75 chevy custom deluxe with the 350 motor and a 3 speed manual transmission. If anyone else out there is also looking to replace their "3 speed on the tree", I have found a kit made by Classic Parts that converts the shifter from the column to the floor, and its rather easy to install. That was one of the weaknesses of the 3 speed chevys, that the shifter assembly tended to wear under the hood, and when the driver shifted from 1st to 2nd gear, the transmission tried to go into both gears at once. I don't mean to seem like an advertisement for Classic Parts, but that kit has made driving alot easier for me!
I used it on my 84 it did work well but make sure to put lock tight where the handle attaches to the linkage that can deffinately put a damper on the drive ablity