Silver button on the center of the needle.
Correct for 1972.
6,250 RPM redline.
The trim ring is rusty.
On these gauges, the trim ring is folded over the edge of the rear housing and the rings are not designed to be easily removed.
Need to find or make a special tool for removing the trim ring.
Lots of markings on the back of the gauge.
The markings I recognize:
6 cylinder
12/71 (manufacturing date of the gauge housing: December 1971)
2.72 (the date that the gauge was assembled to the car: February 1972)
Pretty dirty and rusty...