Footy
I use domestic scales but the kitchen may have a suitable type provided permission can be obtained. You could just rest the keel on the scales with the boat on its side to get an indication.
The rudder is clearly a mod and may not be in the original designed position. On such a short length boat this may be relatively critical. Can you see if there are any marks on the hull suggesting a previous fitting?
Are the sails the original that came with the model?
Dave