To be fully candid, you can't really count on Mach's software based limits to keep you from hitting your physical end limits, there's just too many ways for those limits to get mis-set or ignored.
Its not that hard to put physical limit switches on your machine, take the time to do that, it will definetly pay in the long run.
Get lever switches that are normally closed and wire then in a loop from switch to switch. This way if any of your wiring or connections fail you know right away and failure doesn't disable your limit switch system. This is also the easiest limit system to setup and its simplicity has advantages.
Lever switches are cheap and easy to mount and get set up, just machine some small blocks that mount on the other surface that actuate the levers.
Paul T.