RE: CG Chipmunk mods
I built two, one with flaps and one without. I liked the no-flaps better. Terrific plane either way. I ran an ST .60 in both, very fast but not unlimited vertical (overrated, IMO). The Saito might do it with the right prop.
Personally, I wouldn't go LiPo with the Rx battery. NiMH would save some weight without the extra hassle of charging LiPos. As for the tail feathers, they seem huge already, and I never had trouble knife-edging the plane. In fact, I'd be leery about any mods. I was happy with the stock wing belcranks and the wire-in-tube pushrods. They seemed simple and sturdy, and the planes came out nice and light. The only thing I might do is beef up the landing gear. Just a little.