Provided the base machine is fairly light, and has the 5600lb MTOW increase then you can carry quite a bit of load. A machine on straight floats is around 1600kgs empty and with the mod can takeoff just under 2500kgs.
For amphibs you are looking at another 260kgs (minimum) to your empty weight over the straight floats.
Not to sure what the aircraft is without floats...anyone have any idea?
On another note, Happy New Year too all!