And, the final solution, as provided by [MENTION=20548]JohnDThompson[/MENTION].

I could have just kept the derailleur stuck in position against the hanger. As others have noted, this would make removing the rear wheel a bit problematic. I tried it with the filed down bolt, and found that I could grab the derailleur and twist it back, but this also loosened the bolt. So I'd have to remember to tighten the bolt back up after removing the rear wheel every time...

Or, the extra bolt I had from the second derailleur could be used to do it right. Once I added a 3mm spacer to the freewheel side of the hub, the chain cleared the bolt, but just barely:



I'm not too keen on just barely, and could see a shift in my future jamming the chain against the bolt. A few swipes with a file, and voila:



A very thin plastic washer that came with the derailleur is sandwiched between the derailleur body and the hanger. As John suggested, I adjusted the bolt and nut until there was no slop, but the derailleur could still be swung backwards to clear the freewheel when the rear wheel was removed. Making sure the nut was tightened snugly against the backside of the hanger, I noticed that the bolt and nut did not move when I rotated the derailleur, which is required to get the rear wheel out easily.

The whole process made me appreciate the ease of use of same vintage SunTour derailleurs.

But, Eroica, no? Final build will be very French on an English frame.