On my float planes I balance them with the land gear as per plans. Moving radio gear or adding wait to plane as need to get it correctly balanced. When I install the floats I rebalance the plane this time adding weight to the floats as need to rebalance the plane to the correct location. The imortant thing I find is insuring the step of the floats are 1/2 to 1 inch behind the CG of the plane, and that they are level to the datam line of the aircraft.
Sharpeye