ORIGINAL: LNEWQBAN
The schematic that I attach here is just an additional idea to solve the elevator and ailerons, if you want to be precise.
LNEWQBAN- you cheated - you looked in my basement! I've modified the elevators and ailerons as you have shown in your schematic. Each is 5/8" thick which gives me plenty of room for adjusting the horn's "hole height". Each cutout includes a 3/32" piece of ply on both sides. To align the "horn hole"at the hinge line the screw center is 18 mm back from the LE.
Btw - nice color choice on the schematic.