....
The Mapp gas torch is my best buddy.
....

My smoke wrench has always been the acetylene torch and rose bud. I heat it
till the rust all burns black. Then after its cooled some I squirt WD-40 on.
Then try bolt/nut while still hot. My procedure has been by trial and error.
I've never seen how others do it.

How hot is hot 'nuff? Other things you do?

Karl