If you measure your plane from the drive washer to the rudder hinge line then multiply by .80 that should give you your length...The step should be about 1/4" to 1/2" in front of the C of G Your floats should extend past the nose about 2 " Some guys like a flat bottom , some like a V bottom...If you can find sombody that has a hot wire set up you can easily make some templates out of formica or plywood ..Just rember that the wire can burn into it if its not hard enough..