Earth bolt under Rad snapped....

[Sardonicus]

I would die grind that bit clean weld a washer to the piece poking out put MIG on high setting (this has two purposes, penetration and heat) then weld a nut to the washer (equals more heat) let cool that will wind straight out

[Loubaruch]

The problem with any appreciable heat in that spot is that you are likely to burn and severely weaken the fibreglass. Before taking the Body off route that is major in time and money it could be worth one last try with a centre drill. In the past when trying to release a broken bolt I found that ordinary drills only seem to make things worse by heat hardening the bolt end and they inevitably break. Try a carbide centre drill just to get a pilot hole in the bolt end and use coolant, water if nothing else available If you manage to drill a small pilot try the next size drill and so on only taking a small amount of metal off at each drilling, dont rush and keep a steady hand. Best of luck!

[Sardonicus]

Wont happen the heat will stay localised to the stud/bronken bolt in question and can be quenched straight after this is also beneficial to the froze stud , done this kind of repair many many times

[fieryfred]

If the body is not coming off. Why not drill a new hole in the chassis, waxoil the tube & add a new earth point.
Either captive nut or double nut or Nyloc.

[Loubaruch]

Not as simple as that. The brass bobbin would then need to be moved as it is a main fixing for the front of the car involving re-fibreglassing it in. A bit awkward in that position.