Thanks, Showdown!
I had an epiphany last night, as I was drifting off to sleep. It wasn't a huge epiphany, but it is, I believe, a neat solution to a problem I had been pondering.
On my last eight-string I used four bass tuners and four guitar tuners. That meant I had to drill two differently-sized holes, located different distances from the edge of the headstock. I was planning on doing the same thing for this build too, but instead of using Gotoh and Grover tuners as on my last build, I had planned to dip into my stash of Schaller M4 and M6 tuners.
The M6 tuners are the nylon-bodied variety - I picked them up a while ago for a good price, and was going to use them on my LPDC, but I went with Hipshot tuners instead for that build. So I thought these nylon-bodied M6s would be good lightweight candidates for the eight.
But they're smaller in every dimension than the M4s, which was bugging me. They would have had to be mounted a good deal closer to the edge of the headstock than the M4s, and they are happiest with a headstock that is significantly thinner than what the M4 can take. And I wasn't entirely sure of their ability to stand up to the higher tensions of bass strings. What to do? I could use a bevy of eight M4s, but I like the staggered look of alternating bass and guitar tuners on most eight-strings. Hmmm....
Then, last night, as I was approaching dreamland, I remembered reading somewhere that the shaft design of the M4 and M6 are the same, so that the same buttons will fit either. Bingo! It's so obvious now! Transplant four of the M6 buttons onto the M4 bodies!
This neatly solves all of my problems - a robust M4 body with a smaller M6 button! Now I can break out the drill with confidence!
The only problem with this approach is that I'm left with four of these little freaks: