Thanks everyone for your comments and suggestions. I learned a lot from them. Finally was able to trace the problem to a bad fuse in the right rear panel. Replaced the fuse, jumped the battery, which I think was drained from all the efforts to start the engine, and the engine started. I've replaced the battery, which was quite old. Up and running again, happily driving my XJ8. Thanks again.

 

Which fuse was it? What did the fuse provide voltage to?

 

I believe I should have said "left" rear fuse panel; i.e., the one behind the driver's seat. Fuse replaced was #6, which provides voltage to something called the "reader exciter ECM," which I believe is security-related? Interestingly (to me), I read somewhere in another forum today that this fuse also controls power to the clock in the center console, which explains why the clock stopped (clock is running again). Thanks.

 

The reader/exciter is the module that reads your key and confirms that it is a known key.
Good job! I am glad that you found the problem.