You guys are scaring me about heating up a carb casting. They warp by just being on top of a motor. Maybe Jerry would agree that after getting out the guts, that you bolt it back together to keep it from warping, and don't unbolt till cool.......I would get it out without heating. Very carefully slitting the threads and peeling, if I had to. I have done that with success. Plan B, C and D would be rethread, helicoil and buy a new top. Nice to see that it has the tag.
If it's that corroded/rusted, that the fitting is locked, don't be surprised if it is unbuildable for other reasons.
