Why would the weight make any difference? they both will raise and drop with the fuel level. I doubt one will drop further than the other both being hollow floats.

Google displacement

A heavier float, though it may float, will sit lower making the gauge read low. Now I don't know if the difference between the two matters enough to notice here. Then there is the dampening effect of the heavier vs lighter float.

The float in my 51 a a cork.