I have some great news. I have successfully liberated the first of several Macintoshes.
I decided to take home one of the IIsi's and it's matching Apple Extended Keyboard II. My method for transport from school to home: backpack.
Yes. I carried the IIsi and keyboard like they were textbooks. I placed my actual books in a separate bag and made the 1.5 hour long trip via bus to home. It wasn't fun, the IIsi is no PowerBook.
I tested the IIsi without a monitor (my DB-15 converter hasn't arrived yet) it's outlook is good, getting progressively better after each boot:
Boot 1: Mac II chord followed by the Chimes of Death a few moments later. What do you expect for a computer that hasn't awoken in at least 10 years?
Boot 2: Mac II chord followed by hard drive noise and no death chime. I left it on for about a minute - the hard drive didn't sound like it was loading anything and at one point shut off and then turned back on.
Boot 3: I inserted a boot floppy at this point, but the Mac insisted on an HD boot, producing the same results as Boot 2.
Boot 4: This time it read the floppy (Gamba's SuperBooter) and apparently loaded from it. Eventually I heard an error beep - probably the system-not-shut-down-properly message.
I think it's safe to say that at the very least the motherboard is healthy, although the HD may be dead. I inspected the motherboard - there's nothing very obviously wrong with it, all the caps look fine. Even the .5AA battery hasn't leaked. This IIsi has what I think is a custom PDS riser card installed - at first I thought it was the NuBus converter but it has, connected via ribbon cable, an RJ45 port and some other unfamiliar ports that are placed on the back where the NuBus card's face would be. Yes this card, whatever it is, still has a NuBus or PDS slot on it. Interesting.