I don't think shims are going to be of any use for your situation. As has been said, adjust the 2 nuts at the handle to take out as much slop as you can without making it hard to turn. As for the cross slide screw... take the screw out and turn the nut on it all the way up the length checking the fit in different areas as you go. It's obviously going to have some wear on it but if it's fairly consistent your nut is probably causing most of the backlash. Honestly 0.060 isn't going to stop you from making good parts. As long as you keep your gib snugged up and always take up the slack before starting your cut it shouldn't be an issue. I advocate making some chips with a machine and getting to know it before throwing a bunch of money at it.