I bought a new fuel sender, a sealed unit and all is well after some bending of the arm. My fuel tank is fibreglass so it’s dimensions are likely not the same as a steel tank but they can’t be that much different. The gauge works, maybe half-assed but I now have a good idea of what’s in the tank. I can live with that.
For the juddering on take off in first, it’s possible that the rear rubber damper on the timing cover may have perished which will cause the engine to shake.