FWIW, on my Stinger 60 ARF I have an OS 91FS up front and the elevator and rudder servos in the rear of the fuselage, one above the other, with an elevator bellcrank (from Central Hobbies). To mount the servos I simply opened up the rear section and put a 1/8" ply plate in on each side for a servo mount, and flushed the surface out smooth with some thin balsa sheet. I glued a velcro strip to the fuselage bottom behind the servo tray, and velcro my battery pack to that to establish the balance I wish; I am moving it back incremently with the objective of minimum down elevator inverted. I have no added lead on the airplane (just in my head).