The Berkely plans are a good start but the model kit design is over-built and will build up heavy.
I would make it 2.5 inch to one foot for 40 plus inch span, and build it up using Herr rubber powered plans with the necessary structural beef-ups. The airfoil could be symetrical and use the airfoil use by Don Hutchinson on his Stearman.
I assume you are doing it for stunt. If not, the Midwest Pitts Special produced in the eighties is my favorite for a C/L Scale ship.
Chris...