I'd start by removing the electrical system and hand starting, if the 120 is so equipped. Here's my lightening list:
Remove battery and starter motor.
Remove lights and associated wiring.
Remove any interior lining/furnishing.
Remove flight radio. Replace with handheld + intercom.
Remove any seats and replace with lighter wooden or plastic ones.
Remove instruments. Replace with RAA minimum + existing engine instruments.
That would be about it before you started to get fairly drastic... such as replacing the heavy twin magnetos with modern CDI, for example. The options are in order of preference; easier, bigger savings first and harder, more marginal savings later. The seats and furnishings may be a good first item, though, as they shouldn't affect the CG much (if at all) and will likely net you a reasonable weight saving for minimal outlay and effort. A good example of a lightweight seat would be an old plastic school seat, lightweight ply construction or beach style metal-framed suspended fabric setup.
The empty weight of a 140 is 404kg, and a 120 is more or less an economy 140... so you should be able to come in a fair bit under 404kg empty by removing a few things and replacing others. If you tallied it up you might be surprised at the amount of weight you could easily strip off without too much compromise.
Given the base weight of 404kg and a fuel capacity of 95L/70kg, you have a stock usable load of 126kg after fuel. If you remove the starter and battery that may save you as much as 14~15 kilos. that would increase your usable load up to around the 140kg mark. Lop off lights (we're day VFR only, after all!) and take out the wiring and switches and you might save another 5kg for 145kg usable. Reduce fuel capacity to 80L operational max via dash placard and gauge mark and you would save another 10kg for 155kg usable. After stripping interior furnishings and replacing the seats with lighter ones you may well be able to convince the RAA that you have a legal two-place aircraft.
Cheers - boingk