Voltage limiter
I did the exact same mod on my '66 Barracuda except that I didn't take the fuel gauge apart (as in pulling the face plate) but instead, I drilled a hole in the gauge housing to get access to sterilizing the voltage limiter. I posted some photos here somewhere a couple of years ago. Test to see if your gauges are still good first. If the fuel gauge is bad, you can use it to experiment on.