Do you have the aug 08 issue of Model Aviation. ? If you do there is a drawing on pg. 103 that shows how to set your cg for a biplane.If you don't have this copy ,let me know and I will photocopy and post it for you.Let me know. I will describe the drawing for you. first ,you draw an imaginary line from the center of the leading edge of both upper and lower wings.Go back 25% MAC on both wings.
Draw an imaginary line between these two points next go 50% between the on this imaginary line. This should be close to what would fly right. If the wings are swept back you would have to consider this to,but on a waco I don't think the are.