Hi xintersecty! Thanks so much for replying!

The impact gun I have doesn't seem to come close to having enough force for the stuck bolt. Also, the mechanic that inspected it and tried to get it off thought it was frozen and was surprised when I told him I had turned it. I am assuming he hit it with everything he had impact wise. I guess I could try to heat it and use the impact but I don't want the rubber mount to get damaged. Does anyone know what part the rubber mount is to replace?

I have soaked with liquid wrench multiple times. I will continue to do so. Is there a better product in your opinion?

The other (free, passenger side) bolt feels like the nut is inside the frame in a cage rather than being welded. I will try to take the passenger side off and investigate if I would be able to access and weld the nut at all from the underside. It will be difficult to see since I will have to pry it away from the frame to get any look at all!

Still open to anybody else's ideas as well!

Thanks again, xintersecty!!!! Your car looks great by the way!