If you are using a Gibson and want to replace the Klusons, the non-locking full sized Grover 18:1 machines are direct replacements as far as screw holes go. If you have a modern Gibson, you are set. If you have an older one you may have to widen the hole that the post goes through.
The high ratio Govers are stable, smooth, hold tune perfectly and LOOK vintage (check out Jimmy Page's guitars from the 70's). Sperzels and other brands look a bit too modern for me.