The good news: The CalComp graphics tablet is indeed ADB, and I've now been able to verify that it appears to be in perfect working order aside from the tip of the cordless stylus being badly worn down. However, I only have Aldus IntelliDraw on the G3 Mac, and in the little playing I've done with it thus far, the main thing I've learned about IntelliDraw is that I utterly hate and despise it.
(To name just its two most egregious faults: [1] tools cannot be persistently selected, so every fucking tool reverts to the goddamn selection bandbox after every action (read: every time you lift the stylus tip off the pad surface), which would make it utterly maddening to try to draw freehand with it, and [2] you effectively only get one control handle per B-spline point, and IntelliDraw doesn't even actually let you place the control points, which severely limits the ability to draw Bezier objects -- which is mainly what I wanted to be able to do with it. Memo: When I select a tool, I expect it to bloody well STAY selected until I select something else.)
Knowing those facts, though, and knowng that ADB-USB adapters exist, if I can get hold of such a thing I may be able to get the pad working on my Linux machine, where I have the Gimp. Or maybe I can get my hands on a copy of Freehand for the Mac....
The bad news: I thought I had a 1GB disk and a 4.3GB disk in the aforementioned G3 Mac, and two newer and cooler-running 9GB disks on my desk. The 4.3GB disk isn't 100% reliable and doesn't always spin up (either it has a stiction problem, or it's drawing too much power for the Mac's power supply), so I was going to pull out both disks and replace them with one of the 9GB disks on my desk. Only problem is, it turns out the 9GB disks on my desk are actually 4.3GB, and the unreliable 4.3GB disk in the Mac is actually a 9GB disk. I could put both 4.3GB disks in the Mac, but (a) that defeats the goal of leaving only one disk in the Mac, and (b) I had plans to use one of the two disks on my desk in my Sparcstation LX when I reinstall it. I could pull out the 1GB disk from the Mac and leave just the 9GB, if I trusted the 9GB disk; but given its demonstrated failures to spin up, I don't trust it as a boot disk.
Well, blarg.
Still, at least I now know the two ... er, 4.3GB disks are good.