If you have the resources to buy and then resell a 660Z, surely that would be no more expensive that trying to mod your XTX for the trip and would mean you'd be doing it on a bike well suited to the task. And without risking the condition of youor current steed.
As maxwell123455 says, go slowly and you'll get there on almost anything but that won't necessarily be much fun and proper dirt bikes are more resistant to crash damage eg. dented exhaust pipe.
Of course, do that and you might discover you like the Z and decide to keep it...