attach lead weights to the nose of the floats. That way when you remove them, and put the wheels back on, your Eagle will still balance properly. If you are using the sticky back weights, put a screw or two through them...The adhesive on the wieghts can loosen in the water.

What some guys do is build a small compartment in the nose of the floats, or install a pill bottle, and fill it with lead shot until the model almost balances...then add a generous helping of epoxy to finsih the job and hold everything in place...

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I just re-read your post...the floats have to be mounted so that the step of the floats is slightly behind the cg (of the Eagle) (1/2" or so). They should be installed so that the main wing is at 1 to 2 degrees postive angle to the top deck of the floats. Once the floats are installed, THEN you re-balance.