[murray]

when doing any welding always make sure that the earth is as close to were you are welding
personaly i would disconnect the battery
as far as welding a nut onto the top of the shock
is the thread damaged all the way up it ?
if not use washers as spacers to lift were the nut would sit to a area that still has some thread on it
if it is stripped all the way the i would weld a piece of flat bar with a hole drilled in it this will alloy down the weld mix also it gives you some ware close to attach the earth to.
send me a pm with a contact phone # ill run through it with you as you are in perth