ARG!!! Why can't I just let it die in peace?
It worked for about three days, and now it is dead again! I was setting it up for work this weekend and had no problems. Next time I tried to start it to actually do something useful and it froze. Now it hangs early in the boot process, about five seconds after the chime. At least it didn't wait to die until I had some work half-done on it, so it could have been worse.
I guess that swapping out the keyboard+mouse, video, RAM, PSU, drives, and CPU - that this leaves the board itself. So I broke down and ordered a "new" 166MHz FW400 logic board.