With a torch, heat that end of the bolt until cherry red. Tap on it a little, then loosen as usual.
I second Paul’s fix. I had bolts rusted onto a caliper on my old 69 Mercury. A couple minutes with a torch, a few taps with a hammer, and an impact wrench for good measure, and it broke free real quick. Wear protection or you’ll wind up with white-hot rust and slag on your skin which doesn’t feel good.
When I was millwrighting we would heat a frozen bolt cherry red like you say and then dump water on it and hit it with an impact gun. If that didn’t work we would torch them.