Randy from Zip Dee was a big help.
We discussed the usual scenarios. I had already tried them so we quickly moved on based on photographic evidence he asked for. My situation was odd enough that he sought advice from the installers. Basic problem was that the winding tool couldn't get a grip on the threads of the spring rod. The angle was bad, and I think the threads had been damaged by the previous owner in a failed attempt at repair. Randy came back on the phone and offered two possible solutions:
First option...Disconnect the forward head casting from the arm to try to get a better angle for the winding tool. Turns out there is so much tension in the roller that you can't control it.
On to the second option...
Loosen the through-bolt of the rear head casting, Disconnect the rafter. Place a ladder under the roller to catch it, and get ready to catch the roller, too, as it bounces off the ladder. Find a big stick to leverage the head casting off...dramatically. This is not recommended by Zip Dee except as a last resort. I don't recommend it unless you have no other options. We took precautions to stay out of the way and under the awning. Three or four hard pulls on a three-foot lever, then a lot of noise as the spring unwinds in less than one second, and the roller bounces off the ladder. I catch it. Randy says, "I heard that. Sounds like something happened."
Then it's just a matter of putting it all back together according to the installation instructions...with a helper.
Turns out that the rear rafter had been bent in whatever event caused the damage to the head casting. I'll order that after our upcoming trip.
Randy stayed on the phone with me as I gathered extra tools when needed and two more step ladders. I really appreciated his expertise, his concern for safety, and his patience. After the head casting came off, Randy went through the procedure for putting it on. The call lasted 52 minutes.