Many thanks to all for their replies. Wayne Bingham has offered a spare part that I'm grateful for. For those interested, I put the derailleur back together without the part (didn't want to lose anything more) and the jockey cage wobbles. The bushing is definitely needed for that year's 1974 derailleur.
Dan Artley in Sunny, Much Brighter Baltimore Maryland
<<<While cleaning up a Campy NR rear derailleur, the nylon washer/bushing from the bottom pivot fell to the floor and disappeared into the netherworld of my bike work shop. Profuse cleaning (of the shop) didn't turn it up. Would someone from the list have a line on Part No. 810/1A from the Campy Catalogue No. 17.>>>