On my machine (floated, with my avionic fit, 1148kg empty), with just a pilot, then provided the pilot weighs more than 20kg you will be inside the rear CoG limit.
As Heli190 says, it is very easy to run out of fwd CoG on the 120 if you want to lift 5 guys. Say 4x90kg guys (Pilot and 3 pax) then I have just 60kg left in the final rear seat and then out of fwd CoG.
So weight reduction behind the mast will begin by improving both total payload and flexibility for GoG.