I bought a 1/2 inch feed 1/4 inch return line sending unit, used a step drill to enlarge the 1/4" hole up to the 1/2" size and silver soldered a short piece of 1/2" metal line into the sending unit. The step drill left a small ridge on the opposite side of the hole, which aided in stabilizing the tube I installed. It works great, and you can do the same thing with 3/8" sending units.
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?