I was thinking about doing the same but wasn't sure on how well the old tube and weld around it would drill. Any tips on the soldering? No issues with the sender connection overheating /melting?
I heated up the silver solder that was holding the 1/4" return in place, removed the 1/4" tube and then drilled it. I used a small pair of vice grips and some aluminum foil to heat soak and shield the plastic parts on the sending unit.
Finding real silver solder was the hard part though. The stuff they try to pass for it in hardware stores sucks and is not real silver solder. I ended up having to go to a welding supply store to get the old school stuff.