I have two H9 Caps one with a Moki 180 and one with an OS 160 and love both of them. The Moki seems to take it verticle a little better than the O.S but both are very good choices for the cap. I wouldn't put the servo's in the rear as the plane is kind of tail heavy anyway. I went with dual servo's for elevator on both and put them up front and had no problem getting balance right with the battery pack. I like the Moki and I like the O.S so it's a toss up.If you run the Moki go with no more than 10% nitro 5% is better. I run the O.S. on 10% to give it a little more ooomph. Good luck you will like either engine in the H9 Cap. bob