cali2ia

I tried inserting a 27.2 seatpost into the Louison, as per auchencrow's suggestion, and it was a no-go. That's a shame, because the seatpost is one part that has to go (rusty chrome flaking off ... but only on the exposed section), and 27.2 would mean an easily found replacement from VO.

I had a similar thought as you about the serial number, T-Mar, but I was given some scans from the cyclopedia catalog and the evidence is overwhelming that it's a C-34 with the Huret package. To the original description I would add the the saddle bracket (or whatever it's called) is labeled Ideale, which matches what the C-34 was shipped with.

3.2 MB PDF here: https://palmbreezeproperties.com/Cyclopedia-Bobet.pdf

Google Docs link jere https://docs.google.com/fileview?id=...YzJkZjEw&hl=en

Hush

Seatpost diameter could be 26,4mm on this"old frenchy".
Not too difficult to find .... in France : https://stores.ebay.fr/VINTAGE-BIKE/S...=p4634.c0.m322
Hush

unworthy1

Seat post for metric 531 would be 26.6 or 26.4 (not 27.2, that's Imperial 531)...don't know what metric straight-gauge 531 or Reynolds "A" would take (but a Zeus owner would know, since many of those were metric "A" tubing).
Most people believe that LBs were made by Mercier despite the numbering that's so like Bertin's...however, Norris Lockley (who knows so much about French cycling and the industry) mentions another St. Etienne firm called Cizeron, which he credits with building (at least some of) the LBs.
Whether these are the ones Gene Porteusi imported to the US, or were only for the European market, I don't know.

Wildwood 

For what it's worth my 70s Raleigh Super Course has a 62.5 seattube with a 58.5 top tube. And an 84 or 85 Bianchi Limited with a 62 seat and 58 top. and my 85 Trek series 600 is 63 seat with 58 top. (all measurements are C-C)

the relatively short top tubes are perfect for my 60yo aging frame.

Jay T.

I owned a C-34! For a few months in 1970. It got stolen.

I wanted a 28 or 30 tooth cog on the rear, so Cyclopedia couldn't sell me the Campagnolo Sport derailleur I was interested in. I had them put on the Huret, not being sure how good it would be. I ended up not being satisfied. I would have replaced it with a Simplex and been happier.

I think it came with an Ideal saddle--all nylon.

dbakl

My 3 Zeus bikes are all 26.8 seatposts, for what its worth...