I bulit mine with 30% more rudder area, and the center of effort lower (closer the plane's axis of rotation). Followed the shape of the horizontal stabs. I did the upswept wing tips, but, doing it over, I would go with the straight. The upswept is supposed to cancel the tendency to "Dutch Roll" (a snap roll opposite the rudder input), but I think this may have been due to the original rudder having the area high on the surface. I'm no engineer.

I have talked since to pilots who left out the wing tips entirely, and one even chopped a panel out. Only drawbacl, aparantly, is a faster landing speed. I have an OS-70 II in mine and it is a bit heavy. Plenty of power, but it doesn't need the apron flap to drop plenty fast on approach.

I wouldn't worry about glassing the cowl. It's plenty solid. Mine is coated inside with thinned epoxy and even was a "functional" scoop. The OS has a down-shot rear carb and I built a 1/4" x 3/4" half-round channel into the scoop to supply the carb. from underneath.