I don't have the Cermark Pitts, but a friend does and I have flown it several times. I have a G/P Pitts. The reason for the dual elevator servos is to have a back up in the event that one fails. I can personally attest that you can land a plane safely with the elevator halves in opposite directions. If I had only one servo instead of two, and the one had failed, I would have lost a 30% scale Extra. The servo failed due to old age, and no other reason that I can find. It just wore out.

The ailerons will work just fine using one servo per side of the plane. One for each aileron, making a total of 4 is not necessary. Any good servo of 70 oz inches or better will suffice. Since you are going to run at 6 volts, the aileron speed will be even better. The guy with the Cermark Pitts slaved the ailerons together with 4-40 rods, clevises, and a control horn mounted on each aileron. I didn't note any deficiencies in performance when I flew it. Save the money and wiring and use two servos.