I just spent another 15 minutes beating on it rather severely with a 1 inch dowel between the bold and my hammer, after soaking it with WD40. No change at all. This is intensely frustrating. I had to rebolt the shock back up in order to have a drivable vehicle tomorrow. Not sure what to try next.
The bolt does turn with my socket wrench, though quite stiffly and with a good amount of resistance. The shock is not putting any pressure laterally on the bolt as I can pull it completely free of the top connection point.