RE: 1/2A 150ish Build
I made a "mockup" of the center fuselage section and cut new F1 and F2 formers from balsa to get the angle right for the 1/2" tri-stock. I glued the tristock to the fuse side mockup, and gradually changed the angle with a sanding block, and got it really close(good enough to fit tight). The F1 and F2 formers should be beveled at the top to match the angle of the tri-stock.