Factory tach???

there was also a clock for the center pod in the rallye panels. I know the clock got its 12 volts from the red post on the amp gauge. I'm pretty sure the tach did too. Odds on the tach still working are mighty slim. The needle responce was slow even when it was new. Year One offers a replcement tach but it's a little pricey.
The performance indicater is just a vacuum gauge and was found with every engine / trans combo built. Most of those do still work like new. It is much simpler to test before installing.
I have the clock in my car. I set the neg battery cable off when parked so the clock never shows the correct time unless I reset it. I did put a inline fuse in its power supply.
All of this is just FYI . Any 40 year old gauge might work today and die tomarrow. These panels are no fun to R&R. If I was asked to choose the most dependable gauge, it would be the performance indicater. Good luck either way.