My solution was: a lot of heat
Used my propane torch and to protect brake lines, I covered them with my welders gloves, because I couldn't find any plumbers mats.
Each bolt took around 5-10 minutes of constant heating and then serious impact gun action, but I got there :)
Yeah, constantly checked if nothing was overheating. And the impact did very well too. I am surprised how hot it can get. The impact bit sometimes got too hot to the touch, so I had to stop so it could cool down
Been there, done that. Swapped my motor out on my Mazda6 and the A/C compressor was WELDED on to the old engine block from rust. Sucker added at least four hours to the swap. Getting it out was liberating
When you reassemble, wire brush clean and use an anti-seize compound. A ten buck jar will last years. I use Permatex nickel (silver, white 6 oz jar with brush in cap) for nearly everything.
Mostly it seals out water but the finely ground nickel metal dust does the work.
Also put the nut on the bolt, in your hand, and look at it closely: usually the stuck part is very small, the outside threads. But the nut against the part has a lot of static friction.
Spend time examining parts like this really closely, you'll get a lot of insight into how this happens -- and how to get out of it!