I found the original article where they were described. They were used as speed brakes and flaps. When deflected some of the area deflected up and some down which would increase the profile drag of the airplane. The max deflection was 40 degrees.

Quoting from his article in Model Airplane News, Dec. 1976, he says, "Also highly desirable is the combination dive brakes and landing flaps as shown on the plans. The excellent low speed performance of the Curare is further improved with the flaps."

He was apparently able to use them effectively but he was also an extreme talent at flying.

I have a Curare without the flaps and it is a fun airplane. I doubt ( well no doubt at all) that I do it justice when I fly.