I got the keycap off. Didn't think I could do it, since there didn't look to be enough space for paper clips. Then I tried floss, and even tried knotting it into a pair of loops. The problem was that I couldn't get the floss loops to stay put. Then I got an idea: twisty-ties, the paper-covered wire kind that I get on loaves of bread at the store. Worked great. Took some pulling.
So, what did I find?
I found a little black switch! It has a black slider. The switch says "ALPS" on it. In the center (way down in there) it says "15A", and in the upper right corner it says "15C". The upper left corner has an "N" (for "NeXT"??). The bottom left corner appears to have a "9". This was the "8" key in the numeric pad, on a non-ADB NeXT keyboard. The label on the bottom says Part No: 192.00, NeXT, Inc., Palo Alto, California, Made in Japan. Serial number AAE4209119. Weight seems to be about 2.7 pounds.
I wonder where those Internet sources all got the idea that the NeXT keyboard had buckling springs? I'm guessing that there were only two types of NeXT keyboard, the old ones like mine, and the newer ADB type.
Of course, my other question is what kind of modern switches are comparable to the ones in the NeXT keyboard? Bear in mind that my keyboard is probably at least 16 years old.
David