I've tracked the manifold down to the all-but-one-last-owner, Brad Nauss.
http://www.bradnaussauto.com/He just sold the part to an anonymous buyer:
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To: erwin@rekup.net
Sent: Monday, November 10, 2008 3:51 PM
Subject: Re: Abarth twin-carb intak...
Dear Erwin,
the twin carb set HAS already been sold
I would ask that the only information from me that would be given on the forum, is that I purchased the set at the auction, and it was sold to the first person who saw the ad in the club newsletter.
I will forward your information to the person who is purchasing these. it will be up to him to disclose any more information.
IF you find out more information, as a Citroen collector I would love to know what you find out about its history.....and would forward that to the new owner also.
best wishes, Brad Nauss
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Now we only have to hope that the new owner will take contact, sooner or later...