Sure enough, I couldn't budge it either, so I found a way using a wood clamp. Strange that this is the second time I've employed this wood clamp while working on this vehicle, and it saved me both times.
It may be hard to see from the picture, but I used an offset ratchet and positioned it so that I could wedge the closed wood clamp between it and the frame, and then just gave it a few turns and it broke free easily.
I guess you could leverage it with a pipe or something, but this is what i had laying around and as it turns out, it's perfect for this job.
