After messing about with sandpaper wrapped around drill bits, I got aggravated and grabbed a round rasp. I drew a circle 17/32" around the tuner holes as a guide so i wouldn't rasp egg-shaped holes and went at it v..e..r..y s...l...o...w...l..y until I got a firm thumb press fit on the bushings. Reamer? We don't need no stinkin' reamer!
Used a centering ruler along the neck centerline to align tuners square:
And pre-drilled some shallow holes with a drill bit matching the screw hole diameter in the tuner plate to center the screw bit:
Bam! Came out sweet. These Schaller tuners really are nice.
Strung up E and G strings to see how things lay, no evil surprises. Yay!
Hmmmmm.... Gonna go out on a limb and call my pre-cut brass nut.... a
tad high.

The Axemasters brass nut is, oddly, two pieces of brass glued together, apparently with elmers or something equally useless, because it IMMEDIATELY separated into two pieces when I tried to grind it a little on my bench belt sander. No more of that.
I CA glued it back together and am slowly whittling it down to some approximation of reasonable height using my low-budget fret beveling jig. This will take a good long while, but it's my first full nut fitting.
Another day, another new skill to learn! Any idea how high this nut should be, even a ballpark, prior to doing any fine adjustment by nut slot filing? Any advice or links to good tutorials on nut shaping and polishing greatly appreciated. At least the string slots and top edge seem to have a pre-cut slight cant towards the tuners.