for balancing biplanes, you calculate MAC based on the shadow of the wings when the sun is directly above and the airplane is level. Basicly you are ignoring the area of the lower wing that is directly under the upper.

For example, lets say you have a biplane where the upper and lower wings are identical... but the leading edge of the upper is 1 inch forward of the lower. The MAC would be based on adding 1 inch to the upper wing's trailing edge, and ignoring the rest of the lower wing.

From there, you go back to the standard MAC calculation for a monoplane. Just about anything will fly with the CG at 25% MAC (except Canards and flying wings...) and most its safe to go back to 30%.

Now... you don't need to know what airplane it is... you can come up with a starting CG and fly it.

Noseheavy is slggish to respond and requires a high landing speed. Tailheavy will do a 3/4 loop on takeoff... You can almost always deal with how a noseehwavy plane flys. Tailheavy tends to get "rekitted."