Steve,
You're going through all this renovation. I had a squeaky tach when I bought my car, and after struggling trying to lube the cable, and replace it, I finally figured out that it was internal to the tach. pulled the dash apart, removed the tach and speedo, sent them off to speedometer.com in Texas, they opened them up and replaced a gear in the tach, and lubed the inside, and now I have no problems. If I were you, I'd suck it up and do a complete job. While you have the dash apart, change the lights to LED's so you can see the dash at night, fix the rheostat (or disable) for the dimmer, and then never have to worry about them again.
My two cents.
Mike Mizesko