JRI wrote: the model was designated as 40cc that my 55cc 3W up front will balance out the servos, otherwise it might be a late night visit to the local church roof! Also I have an inboard tuned pipe which might well have cooked the spaghetti of plastic guide tubes.
Re JT's comments on Scale models - Suspect a large proportion of your tuned pipe will sit aft the C of G which will counter the heavier motor. So fitting servos aft could be detrimental.
BTW - Given the installation problems you have - Don't be tempted to reduce the moment arm on the control horns for "scale effect"
(Frank tried this on the Provosts rudder but the pull pull wires had no authority on the control surface so i have had to surgically remove it and rework)