I gave up after four more LBC's. At least one had a guy who remembered the part.
So, at the last LBC -- I actually rode there so I'd have the bike with me -- I bought a rack, rated at 55LB but still only 4" wide, thus I can mount the twin baskets directly to it. And they installed it for free; otherwise, I'd have had an interesting time getting it home.
Pretty much ready to resume shopping on the bike.
Thanks, everyone, for the input!
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Larry:1958 Drysdale, 1961 Gitane Gran Sport, 1974 Zeus track, 1988 Masi Gran Corsa, 1974 Falcon, 1980 Palo Alto, 198? Vitus 979. Susan: 1976 Windsor Profesional.