[oldE]

Yes, I have certainly thought of such a rig. You couldn't build one for that price. Hmmm. I have the drive unit from a bush cutter ......
Food for thought.
In the meantime, I got a line this morning which works. Husqvarna 0.105 "professional". I took the bobbin with me and tried the available lines until I got one which fit properly. When I got home I got another 300 yards done on a tank of gas. There's only about another 150 yards to go, but it is where the tractor couldn't go, so I'll be cutting a path as I go.
Follow up: I managed to get the tractor and bush cutter into the soft area from the other side for a ways so only had to cut a path through about 30 yards. I managed to get the remaining sections done before it got too hot this morning.