The guitar seller warned me that a Tuning machine (G string) is a bit tough. If I wanted to change all tuning mavhines instrument which should I install?
I'm not aware of any good tuner replacements that mount with two screws, above and below the tuner, as the "wafflebacks" do.
It's possible that good set of Grover 18:1s, with the tuner screw-hole tab in the center, MAY line up with bottom screw hole.
If not, you'll have to decide whether or not to fill the old screw holes and drill new ones to accommodate a quality set of tuners. (Some people here are *very* queasy about doing that!)
I can't abide mediocre tuners myself. On my favorite guitars, ones I expect to spend a lot of time with, I have no qualms whatever about replacing 'em. (My favorites are Gotoh Delta 510s, with 21:1 tuning ratio.)
The D60 is a darn nice guitar -- congrats!