Hi there, have you looked at Sailplane servos? They're built small with tabs to mount them flat in a thin wing. You'll still have to do some surgery and build a servo tray for them.This was my first hit in google querying <sailplane servo>
If you try it go light on the elevator mix. A little bit goes a loooonnggg way.
I always mix in too much and then when I hit the switch the plane dives like a
Stuka on a bombing run