'69 Big Block HP Exhaust manifolds - Sleeve nuts rounded off. How can I get them out?

[Dutchrebuild]

Last time I had a manifold giving me that much hassle, I beat the ******* thing to pieces with a sledge hammer

 

[MikeyM]

Thanks for the suggestions.

RJ - Seems to me it would be a hell of a lot easier if the stud came out. I have the replacement fasteners so I'm totally good with that. So drain the coolant down past the stud or all of it? How hot would I need to get the stud for it to come out? Are we talking glowing? I just picked up a temp reader so I think I can get pretty close if I have the right gas.

Thanks,
Mikey