I am working on a -6 conversion, a '73.5 2.4T to be exact. Obviously a tach from a 73.5 2.4T would work, but will other 911 tachs work? Does it matter (other than redline) if it is from a T, E, S as long as it is from a 3 pin CD box?

I think any 911 tach from a 3 pin box will work. It so happens I have one if you're looking. I'm going from a 2.4 to a 3.0 and won't need it. I paid 50, tore it down, cleaned it, polished the lens and repainted the bezel....yours for 65. PM me if interested.