There is a low pressure area located on an airfoil at moderate angles of attack, on the forward top surface. This distribution would tend to lift the leading edge up.

Hitec I believe have a 90 oz-in retract servo available, but you are right that space might be a problem. I'd stay away from a torque rod arrangement, if I were doing it, but that would allow you to keep the servos inside the fuselage or LEX). Perhaps a couple of air cylinders along the span is the way to go, as previously suggested. I'm assuming this is the big F-18 kit?