Hi Ralph,
The gas gauge has always bounced and increased its active jumping as the fuel gets lower in the tank.
I still have my original float and many have increased the bounce by NOT installing the sending unit with the float toward the front of the tank. Originally, the ground for the sending unit is provided by fuel pump mounting and as connected through the metal fuel line going from the tank to the pump. When some have installed a fuel filter between the tank and pump, the original ground is usually lost. If the gauge still works, it is because a less secure ground was found through another connection someplace or a replacement ground was connected to one of the sending unit housing nuts. In either case, a ground, weak or strong, was present for the gauge to work.
One last point. The SU fuel pump uses a coil in its operation and, although it is a 12V unit, the effect of the coil induces voltage to as much as 10 times that amount. With the installation of a TSV diode that grounds anything ove4 23 Volts to ground, I have found the gas gauge to be a little less jumpy (not as stable as in a modern gauge). Although I can't say that the reduction in induced voltage within the fuel pump has any affect on fuel gauge reaction, it is possible and my points longevity and pump reliability is a result of this addition.
Although you can add a circuit that will stabilize your fuel reading bounce by slowing and short-time averaging response, I have found that the original was not that bad and, other then the needle needing a tap when the car first started, I feel the gauge bounce is another reflection of the raw temperament of the car that I like.
All the best,
Ray(64BJ8P1)