Perhaps a moderator will move this thread to the Exhaust sub-forum.
All exhaust fastener threads, and under the nuts/bolt heads.
No such thing as "MAP" gas.
A dozen years ago, MAPP gas was discontinued. It was hotter than propane. Worked nice for soldering copper tubes. To replace MAPP, they're now using fraudulent, deceptive advertising to sell "MAP-Pro", which is useless. Not much hotter than propane, and propane without extra oxygen is good for burning deposits off of spark plugs, lighting bonfires, and not much else.
You're working on exhaust items. You need additional oxygen. I've heard Oxy-Propane works OK, but I've never used it. I use Oxy-Acetylene, which kicks ass. Beyond flame heat, I've used a MIG welder to weld nuts onto broken bolts, which works pretty fair.
If you just go in expecting every stud to snap, and every bolt to break...you'll finish the job faster than you expected.
My '97 K2500 7.4L has at least two broken exhaust manifold studs, and I haven't even tried to remove the manifolds. The studs popped on their own.
How are you planning to attach the sheet-metal spark-plug heat shields? Will they even fit?