I'm with David the Wreckrman here....it's not a 3D ship...I've owned 2 of them....still own one of the 2(see my avatar)...I have .91 4-stroke in mine....and it's a VERY nice flying plane, totally unlimited in most anything, EXCEPT 3-D...fo get ab ouut it...forget it. Sure she'll hover some, and knife edge til cows come home....and tumble...wow..all kinds of em... but harrier...nope... torque roll LOL...it won't do any of the high alpha manuevers...at least not like other true 3D capable planes. That plane was designed before 3D was as common place as it is today...matter of fact, no one outside of the TOC competitors were doing it when that .40size Extra was kitted...and I don't think even TOC was doing 3D yet.
Don't get me wrong here...I really really like my Extra..it just wont do those types of aerobatics.

If you must try though....change the hinge lines, less stabilizer areas,, stuff like that......don't just add control surface...the whole hinge lines, to and include the aileron must be changed...a bunch....to sit and figure it out though....I'd go choose another plane in less time. Just my take on my experience with my favorite plane here. I don't want to discourage you, but dont want to here of someone that was disappointed either....but I've been proven wrong before too, so if you do decide to take this on...I wish you the best..