RE: CG of a biwing
This is what I have used on my bipes, even my Midwest Super Stearmen, which if you used the CG on the plan, you had an unflyable airplane.
Set the plane close to level.
Plumb a line vertical from the leading edge of the upper wing, make a mark.
Plumb a line vertical from the trailing edge of the lower wing, make a mark.
Measure the distance between the two marks, and use 25 to 30% of that measurement, measured from the leading edge of the upper wing.
This only works with straight wing bipes.
Ken