With regard to your elevator servos. Do not set them up the way you suggested. You will most likely end up with a differential throw, causing you more trouble than you can imagine. Spend the money and get a JR Match box, or one by another manufacturer. Makes life a lot simpler.

As far as the ailerons go, two servos will work fine. Might I suggest a servo that is relatively fast (.20sec/60deg. or faster), and around 70 oz in of torque, or better. I personally prefer a digital servo for better centering resolution, speed, and torque. I watched a Cermark Pitts strip out two standard Futaba servos on the first flight of both the plane and the servos. Plane was saved by a very good and quick thinking pilot using rudder/elevator only from that point to the landing.

I don't remember the month of issue, but one of the kit reviews of this plane (R.C.M. or M.A.N.) used the two servo set up with no problems at all. The full scale Pitts' has aileron slave struts anyway.