The closest you can get it, is around 0.001" clearance on each side, or 0.002" overall. Any tighter, and I have found problems arising. You can mash the slide rails in with a vise or a fixture, then use a good lapping compound to free it up, and obtain the value, but that close of a fitting tolerance is only applicable for match pistols, as any grit or dirt may foul it in the field.
If it shoots great right now, I wouldn't tip it.