Any work involving the sender floats involves risks to the accuracy of the fuel gauge. It's all very delicate on the face of it. The critical thing is that the floats are completely unobstructed throughout their full-to-empty travel and that their rheostats are working right.
There's a write up on the rheostats here:
http://www.the75andztclub.co.uk/foru...d.php?t=194156
You could also check their resistance range to get more info on their performance.
You'll get more response to this sort of query if you post it in the Technical Help Forum.
TC