Paul , I would mount the Elevator and Rudder servos as far forward as you can , The Ziroli DC3's tend to build heavy in the tail and usualy require a lot of nose weight .
I have mounted my servos just ahead of the trailing edge of the wing in the fuselage , and will have enough room to place the fuel tank on the CG forward of the servo's
I will try to post pics sometime this weekend.
Chris