i would go to at least a 4 or 5mm pitch and change the gearing to retain the ratio. it's possible to use a flanged nut and mount it from one side, as the original is mounted this way. I've replaced a full set of ballscrews on the 260 and had a nightmare to get the nuts sorted. I'm currently helping a friend replace a 240 x axis ballscrew with a standard flanged nut and all looks good so far.