I can be done but you need to change gear ratio's. You have the 4.1 gears and cat makes a 3.6 gear that has what they call a truf saver rear diff, kind of like a auto locker (this came in the 700 xtx's). So you would need to change both the front and rear gears so they would still match, then you may need to do a little clutching to compensate for the higher gear ratio.
I personally hated the turf saver that came in my 700, it cause jerky take offs when in 2wd. However I never use mine for work or on the lawn so I replace it with the spool type gears that you have in your 650.