RE: float plane question please:
Set up the floats so that the step is just a bit aft of the CG - perhaps about 1/2 inch or so. It isn't super-critical, but you should have about 2 inches of float in front of the propeller.
Also, you should ensure that the wing has about 2 degrees of positive incidence relative to the float datum line - that is, when the plane is sitting on the water, the wing should be angled 2 degrees up from the surface of the water.
I assume the plane is balanced with the wheels on as it is. Good. Now, mount the floats and hang the plane on your balancer. Add weights to the bow or stern of the FLOATS to get it balanced. Epoxy the weights in place once you know how much you need. Always put the weights on the floats, so that when you take the floats off the plane will still balance with its wheels.
A good 46-class engine is plenty for a 40-size plane on floats. You might want to put a different prop on, though. If you are using a 10x6 now, you might try an 11x5 for floats. Float planes are not about speed, so you kind of want "low gear" for pulling power rather than "high gear" for top speed.