From the Factory Service Manual it sounds perfect for my type of driving...except it apparently can't be found or had.

So the question is what currently available product is the equivalent of Mopar Engine Oil Supplement?

I presume your XJ service manual is at least 11 years old so just about any API gasoline rated oil today will be superior to motor oil and/or supplements of 11+ years ago.

It was basically the same as the GM EOS. Motor oil with a huge gob of Zinc and Phosphorus added for valvetrain break-in. Perhaps some other stuff, who knows.
You can probably come pretty close by running Rotella or Delvac.

The GM version has been replaced by an 'assembly lube' this is what the old Part number is now cross referenced to:
http://www.gmpartsdirect.com/results...partnumber=EOS
the Mopar version is gone entirely.

Yeah...93 copyright.

Spreading the Revealed Wisdom of Man Law.

Thanks.