Ok thanks for the sugestiuons as I have thought of those ones.The mounting surface inside the stab is 1/4 ply rib.This is a large gas powered plane and the pull if I put screws on an angle might not hold.If I made a plate to incase the mounting flange of the servos say out of 1/8" 5ply it would move the servo out of line with the control horn on the elevators by 1/8".Would like to keep it all in line but strong.Here is my best thought to date is cut out one end of the servo mounting surface(same as both sides),gluing in a plate on the underside say 1/16 ply replacing the rib portion that has been cut out with a new cut of 1/4 ply to inclose the hole for better servo mounting surface and then a 1/32 cap around the top to inclose it and keep it all smooth for mounting of the servo's.With that way it would be like a sandwich with a bottom 1/16 mounted to the existing rib on to the new 1/4 fill piece with a cap of 1/32 to keep it smooth as well as to give bite from top and bottom to hold the 1/4 piece from moving.