Roll with fairings
I had/have the same problem on my -6. I flew the airplane for over a year without the fairings, partly because of yaw and roll problems when I finally got around to fitting them up. I did a lot of experimenting with them to try and figure out the best place to set them up. I did several flights where I intentionally "mis-aligned" the leg fairings a little to see if I could straighten out the airplane. I basically was trying to make the fairings into a trim tab of sorts. I could trim out the roll, or the yaw, but not both due to the inherent aerodynamics. I even tried flying with the leg fairings on only loosely, so the fairings would streamline with the relative wind. That sort of worked, but it didn't lead to a perfectly straight-flying airplane. The end result was that I found a position that was decent compromise at cruise speeds, so I went with that.
So for a data point, I had the same kind of problem. Aerodynamics are funny like that. Even stuff like the propellers slip-stream impacting the wheel pants and fairing can have an effect, so even perfectly aligned fairings can induce some yaw by their very presence.
Good luck!