A mig welder would be the easy way,. just keep blobbing the end of the stud and the heating and cooling will break it loose,.
To drill them,. i,d use a grinder and flatten the nub off, then center punch it,.
I,ve had good luck in bad situations, where i drill the hole right thru and use a 5/16ths nut and bolt,.
as for the donuts, hit them with a hammer and chisel collapsing them into the hole,.
when i did mine i used the hot wrench till things were a nice red colour, yanked the nuts off,. then poured the heat to the manifold and changed the studs,.
gotta love living in the rust belt with a 20 yr old pkup.
1999 chev suburban C2500
300,000 mi