so i just took the heatshield off.. first two studs broken off (obviously a long time ago) and missing

and of course that's where i sprang my leak..
the rest are SOOOO corroded..
Looks like i have a task ahead of me
I am not real flash at getting broken studs out.. especially when they snap off in the head (never done one like that before) are there some tricks i can use?
Last time i broke one off I tried easy (hard) outs, then vice grips, then swore, then welded a big nut to the stump that was left, the whole stud was glowing hot , then i poured water on it to cool it down, it came out really easy after that. Almost finger tight.
Wondering if i just jump the gun and do similar to all the studs (that are left) and replace the lot?
after looking I reckon I will break off more than 50% of them if i just try to undo the nuts.
I have :
gasless mig welder
lpg blow torch
tap and die set (not sure if i have the right sizes) and last time i used one was at school 14 odd years ago..
various drill bits
buying a drill lol lost my last one :(
I think i have to give it a go.. I cant justify the dollars (to myself or the handbrake) to pay someone to do it.
While it's off i can do the egt sensor.