So, I built a Bill Simons Shoestring. The thing just wouldn't track no matter what I did (and trust me, I tried pretty much everything I could think of and some stuff I invented for the occasion. I couldn't get away from the idea that the problem was the stab. Checking with an incidence meter said it was was find, but by eye, it looked like it had a twist. As Conan Doyle said, once you eliminate everything else, what's left, no matter how improbable, has to be the answer.
So, I started building a new stab and elevators yesterday. I will cut the old stab out and put in a new one then refinish the tail and hopefully, that will do the trick and I'll have a classic plane again.
Ooops, forgot the picture.