LOL ..... it pays not to get in a rush and think things through. If you have any questions, feel free to ask.Mark, thanks for the admonition and encouragement. I went back, rethought the problem, and got it unscrewed without a pipe wrench. I actually used a small screw, a bit of copper sheet, and my big-ass Knipex gas pliers. I knew they were worth the money!
The very thin coating of surface rust on the screw shaft inside the bushing was enough to really lock it tight. I cleaned it up and now it runs very smoothly.