Thats crap. Sorry to hear about the mess your in. I had them convert my amp gauge to volt gauge, and bought the solid state voltage limiter. The problem I have is the gauges all "hunt" with the needles of volt, temp and fuel gauges moving together gradually up and down. Almost a 1/4 tank of fuel difference between high and low of the needle swing.
I am planning on switching back to an OEM voltage limiter to see if there is a difference.
I had a similar problem as you, but with the dash pad.
If you need a replacement amp gauge I believe I have one of the newer 72-74 style. I will give it to you for free if you plan to use it (not for resale). Let me know, send a pm if interested.