I sniped the end of the contact points off and bench tested the fuel gauge .. It worked great . once in the car -no fuel gauge reading ..Somehow disable it. There is likely --as Cracked back says-- more than one way to skin that cat. Cut/ bend, carefully remove/ block the moveable contact in the regulator so it can no longer function. bend it open and pump 50-60 lbs of RTV into the contacts LOL Google this there use to be photos of what you are "into."
This is the incorrect year for you but shows what you are up against
Voltage limiter, fuel & temp gauges, '66 Sport Fury
I sniped the end of the contact points off and bench tested the fuel gauge .. It worked great . once in the car -no fuel gauge reading ..