RE: WACO YMF
Dan,
Take a look at the full size wing tip pictures I posted back on page 110, post 2728, they may help you visualize your situation. The plans show the Ribs W-7 and W-8 attached to W-13 in the rear and the Big Tip Block in the front. W-13 should project past W-8 slightly to blend in with W-9 Tip piece. The wing tips taper slightly on top from the last W-6 to the tip and much more on the bottom. The taper on the bottom (of W-13) of the real wing starts about halfway between the last 2 W-6 Ribs and continues to the tip. It seems to give that section washout as the bottom of the ribs taper up towards the rear more than at the front.
The aileron skins look very, very good, what thickness of aluminum are you using? Roof flashing I think is too thick but would be good because it can be obtained in small rolls for a continuous surface. You may need to make the wood core of your aileron a little smaller for the skins to meet at the trailing edge like they do on the real ones.