ORIGINAL: Newc
My delimma is still where is the CG on the plane.
Since your question is "where is the CG", not "where should the CG be?" there's no need to get all worked up about mean effective (or aerodynamic) chords, etc. The CG is simply where chordwise the plane balances.
Hold the plane with a finger under each wing on each side of the fuselage such that the plane is level. That's where the CG is. Then use this point to establish that the step should be 0.5" back.
As mentioned, also make sure that the wing is 1 - 2 degrees positive incidence relative to the floats.
Perhaps I am missing something. If your balance point or CG, whatever you want to call it, is off, aligning the floats to this incorrect point will not fix the problem. I think one needs to know the location of the PROPER CG/balance point before you can properly align the step of the floats. I agree with the post above that you can find the CURRENT balance point/CG of anything by trial and error. Whether or not it is the correct location is another thing. I would start over with this setup. Find the formula for MAC and LEMAC online. The other option would be to take a rough guess. Once you think you have the proper CG, you can mark it and align the step of the floats to it. Then, when the floats are mounted, you have to re-balance the plane/floats to get the CG back to the location you found without the floats. Usually floats require "nose" weight because so much weight is added behind the CG. Just my opinion...