Success! Milestone achieved! All remaining broken head studs removed by MIG welding a nut on.
First we cleaned each broken stud to bare metal, then placed a cylinder base gasket to protect the surface, then a washer, then a nut with washers positioned to level the nut.
Note my favorite blue dress shirt positioned to protect the case etc
Welding generated enough heat to help break the bond and success; all studs backed out easily with little effort and threads intact
I big thanks to mhicks for expert welding skill!!
