I would second the contact Dan Booth.
i replaced the cable in my 67 Avanti II. The Cable was ok but the housing was broken. I took a few pictures but deleted most of them after I was done and the turn signals were working. The switch had gotten water in it and was stuck, I think that caused the plastic housing to break.
The steering wheel and top portion of the column will need to be removed. The first mistake I made was pulling the cable out the bottom and not attaching a wire to snake the new cable back in. I like fishing but not when they are not biting but after many attempts and a couple of bait changes I got a piece of bailing/mechanics wire up thru the column. Then was able to pull the new cable in.
As best I remember I did a lot of google searching and found some write-ups for Oldsmobile and Buicks with the similar Saginaw tilt column's.
Steve
This is where the black plastic housing was broken. This is the top of the cable.
The new cable has a metal housing
These are the only pictures I saved.