Silver braze is pretty easy. Like soldering clean it well use proper flux. What I was thinking is that with a new tank you could silver braze an AN fitting into the thank near the sender hole. That hole will of course give you access.
Harris Safety-Silv 56 Brazing Kit 56KPOP
This might seem expensive but it's darn handy to have around. As a former HVAC guy I used that occasionally. Silver braze flows well, a lot better than brass, and doesn't require quite as much heat. I always used oxy-acet, but I'm told you can get by with something like a MAPP torch
