I can tell you that I had trouble getting the CG back far enough on my YS powered Burrito. I put in a 2000mah pack as far back in the wing as I could and still had to add an ounce in the tail to get it to balance where I wanted it. That is with an APC prop, a Dubro aluminum spinner nut and a thin Higley brass jam nut. I can replace the APC with wood and trade the spinner nut and lock nut for a standard nut and it is about right without the extra weight in the tail. The bad part is starting by hand since there isn't any spinner for my starter with that setup.
I have another Burrito kit that will either go E-power or it will go light with a Webra50 and some lightening work here and there.
I think both tail servos mounted in the tail may be too much back there to balance even with YS 63.
Later,,,Matt