Joined: Jan 2010
Posts: 9,781
Likes: 1,750
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
Funny about the seatpost size, 23.8mm. That's equal to 15/16"!
Weirdly enough, I've got two FRENCH posts in that size (both are all-alloy, with "one-piece" style head).
One is a JPRoutens from a 1980's lower mid-level Peugeot. It uses an inverted rocking head with two slim 5mm bolts, and fit my snappy 1979 UO9 SuperSport perfectly.
Another is a Stronglight, decently long and strong compared to the JPR post.
I bought it 14 years ago thru the former bikeswap.com for my older-style 1978 U09, which it fit perfectly. It's a more normal 1-bolt post.