I just checked out the movement,
That would suggest that your "home made" aileron connector horns are made LOTS better than the ARF supplied ones. Anything you do to move the connect points closer to a better position than the ARF has given us, is going to be a good thing.
any differential would just equate to a little extra drag, right?
Actually, probably more than just a little extra drag. The ailerons on that a/c only have to move about 10mm to give good roll rate. A difference in lift side-to-side probably does as much as a difference in drag side-to-side to make the a/c unpredictable and hard to sort. And everyone knows pretty much to look for adverse yaw and how to fix it.
But you hit it spot on. Fly it and see what it does.
BTW, the guy who posted his idea that the CG was screwed was triggered by his Ultimate having crashed on it's first flight. And my guess of why it did leans pretty heavy on what surface throws he had on the bird. I'd say that the aileron connection screw up would make any biplane a lot more prone to snap when it wants to, not when you want.
I thought the other guy checked it all out using your figures and decided the WM people forgot to allow for the wing sweep
Actually, I don't think he's seen my reasoning and figures yet. And from what he said, I think he was the one who forget about the sweep. I'm guessing he didn't figure on either the sweep or the stagger. For him to figure the proper CG was forward of the WM location, he had to have been figuring his location without one or the other or both.