RE: Joining a V-Tail
Overlap - If you look at the pictures in post 2, you can see that the initial layout pattern is squares that are 3/8 wide and 3/8" long. In post 6 picture, the arc of the airfoil is added to the length and drawn with the leading edge and trailing edge aligned with the layout squares. The overall length is dependent on the thickness of the airfoil primarily and somewhat with the angle of the cut for the V.
(it's actually the Cosine of 30 degrees, but since that is 87% of the thickness of a very thin surface - what with the pen line thickness (twice) and cutting errors, I just added half the thickness of the airfoil.)
So the answer is that you cut out of the center (2 x 3/8") plus the thickness of the stab (1/4"). So in my case 1.0 inches is added to the initial span of the flat stab.
BTW, stab area is not all that critical anyway since we fly light weight models with the tank on the CG with almost no control throw. We get away with it since the center of lift and the CG are practically on top of each other.