Thanks to John's suggestion, I was able to retrieve the washer and nut, although through the oil pan drain. I tried in front, but they had already migrated to just under the oil pump pickup. i had to manipulate them with the "magnet on a stick", then grab them with a needlenose.
Even though I had the locknut, I ended up with using the original jam nut with locktite, brcause I had so much friction tightening the locknut that the special washer kept getting knocked up out of the keyway. I used the red full-strength Loc-tite.
I can't blame this on any PO, because I had previouly re-built the pump due to the dreaded "leaking past the pump seal" syndrome. (Thank you to the forum to helping me figure that out.)
On the previous rebuild, I had remembered to bend the washer up against the nut, but apparently not well enouth. This time, I used the red Loc-tite, and bent the washer up on two sides, crimping it home with the channel-locks.
Hopefulli, I will not have to deal with this agaain, and it will be my childrens' problem if it happens again, (My son and daugheter have both laid a claim to Eddie - she has been in the family since first purchased.)
Thanks again to all responders. I'd have a much tougher time without you!