Stock manifold trouble

[Hankrebel]

71 Swinger 318
I'm trying to remove the stock manifolds to install headers.
1. Any ideas for removing the bottom collector bolt on the passenger side.? One of the nuts is
stripped and and I don't have the clearance to grip it with anything.
2. What is the large hole for on this header flange?

 

[Dartfreak75]

Torch it.Torch the nut off Then when the manifold is off you can remove the stud.

 

[RustyRatRod]

Cut the pipe and remove it with the manifold. That large hole is probably for a sending unit of some sort. If you don't know what it's for, chances are pretty high you don't have whatever it's there for so it doesn't really matter, does it?