The tank was held in place by two U-bolts and dropped away quite easily after the filler pipe and tank sender unit had been disconnected.
My assistant relaxed and watched in the unaccustomed sunshine . . . . . . shortly after the weather returned to normal and we had five days of cold and rain.
The fuel level sender unit was removed - only one screw broke off! Bolts are the popular and readily obtainable(?) steel 3BA size. I was lucky this time - all six broke off from the replacement tank fitted two years later
Chronos (UK) had 3BA screws in stock; other firms seem to have a minimum order requirement.
The pivot was seized but once freed off - Plus Gas and time - the unit worked well and the resistance operated smoothly.
A check proved that the wiring and the repaired gauge was working.