Reddit mentions of Cal-Hawk 2-pc. Tapered Reamer Set

I did this on my Epi SG Jr earlier this year and it’s a game changer. Definitely go for it. I love the Kluson “Safety Post” tuners on my Jazzmaster so I bought a set of those ($42 on Reverb) — just be sure whatever you buy is 3x3 and not 6-in-Line.

If you’re reasonably comfortable with basic tools it’s an easy upgrade. I posted notes and pictures if that’s helpful. The basic steps:

1. Remove old tuners — easy enough with a screwdriver, but the bushings were hard to pry out of the holes. I used a very tiny screwdriver (like eyeglass size) and very, very carefully pried them up until I could get them out. take a picture of the original tuners — 3x3 tuners have a specific orientation and the picture will help you line it up properly.
   
2. Test the new tuner bushings. If they don’t fit, you’ll need to widen the holes with a tapered reamer. I bought this one and it was great. Keep checking it against the bushing every 1-2 turns until you’ve got it.
   
3. The scariest part was that you need to drill small pilot holes in the back of the headstock for the new tuners. Use a sharpie through the new tuners’ screw holes to mark the spot. hold one of the screws up against your smallest drill bit so that the head of the screw is up over the point of the bit. Then wrap a piece of tape (ideally something with a bright color) around the drill bit where the screw ends — that’s how you will know not to go too deep.
   
4. Once you’ve got the holes drilled, then it’s just a question of screwing in the new tuners. I felt like it was safer to do this by hand than with a power driver.

A wide taper reamer?

I've also seen things called a "stepless drill bit" that might do.