A step down transformer is still not a recommended safe practise for a number of reasons:
A transformer will not alter the Frequency, 60 Hz in is still 60 Hz out. The PC is designed for only 50Hz. Therefore it's going to run about 20% faster/hotter than design and thus shorten it's life.
When a transformer steps down the voltage, (240 to 110/120) it steps up the available current. It's the volts that jolts but it's the mills (milliamps) that kills.
If the case/wiring/motor on the PC shorts out for any reason the danger is that the supply doesn't recognize the hazardous situation since it is isolated from the load by the transformer, thus you have litle or no protection if a short develops.
Since you would be using the PC out of doors with an extension lead and isolation transformer I strongly recommend you explore alternatives.
We don't want to see a fellow AG enthusiast doing the shaking and wobbling while connected to the AC main, that's best left for the machine.
Is there no similar device available over there, or an export model from PC?