Catalytic Help

Welp, I spent a few hours under my XJ trying to replace the cat, muffler and tailpipe and was thwarted by rusted bolts at the cat flange.

Everything else is going to be replaced with new hardware so I can cut the old stuff out but the bolts that are holding the cat to the flange where it meets with the downpipe are seized. Bad. PB Blaster, brute force and heat have all been applied and no dice.

So my question is this: what's the best way to get those bolts out? Is the flange threaded or is there a really low profile nut on the other side? Should I drill it out?

My local garage does not install customer sourced parts so I've got exhaust parts all over my house.

Get the bolt nice and cherry red hot with a torch and it will either let the nut go or twist off. Either way you'd be getting to where you need to be. Otherwise a sawsall is my preferred tool.

X2 on the Red Hot Cherry !