Well, I got the two antibacklash nut mounting blocks I needed to make for sure done this morning. (The third I may be able to mount directly in the slide by machining the slide itself.) I gave up on all the fancy stuff for tapping those 6-32 holes and just used a regular flat handle. The key seems to be that you take it in until it gets a tiny bit more resistance, then back it off a full 3/4 turn every time. If at 3/4 turn it is not spinning freely completely remove the tap and blow the chips out. I tapped 4 holes with the same tap with no problems. All by hand without a hand tapper tool.
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I'll use a brand new fresh tap for the slide itself since I sure don't want to leave a broken tap in that. Lots of WD-40 every time I backed out the tap.