It's possible, sure. Mach 3 will compensate for the backlash, but it's best to get it as low as possible first. Even with ballscrews, I have .003"-.008" backlash in my axes....most of that, I believe, is from the lovejoy couplers. If you put an anti-backlash nut setup on the stock lead screw and use zero-backlash couplers, you could probably reduce the slop to an acceptable level.
For me, the mounts included with the fusion kit sealed the deal. Very nice fit/finish. The ballscrews themselves aren't too terribly expensive if you turn the ends yourself. You can always make your own mounts for now and upgrade to ballscrews later.