A few months ago I had to replace the fuel pump in my 1g and was worried I would break studs. At the time I thought the simplest and cleanest solution would be to drill out any broken studs and then have a "C" shaped steel ring made with the correct hole pattern drilled into it. Studs (machine screws with the heads welded on the back side) could be put at any location where there was a broken stud and the "C" shape would allow you to place the whole assembly into the tank with the studs poking up. A couple of flat head screws or even rivets could easily hold it in place before the sending unit got bolted back up
Fortunately I never got to test the idea because I got lucky and none of the studs broke