I do not have a definitive answer to this, but have studied Merciers a bit since buying my own, so this may help.
In 1973, Simplex dropouts did not have the "standard" type gear hanger we see now - it was specifically designed for Simplex derailleurs. It was only in the late 70s that Simplex dropouts came with a hanger that would take a Campagnolo gear without modification. So the rear derailleur is not original - either the dropout is modified to take it or the frame is later than 1973.
Through the 1960s and early 70s, I think the top tier Merciers were fitted with Simplex gears. At some point in the 1970s they seem to have changed to Campagnolo gears and Campagnolo dropouts. However top or almost top tier Merciers I have seen from the early 80s have Simplex dropouts with Campagnolo gears. My own 1977 frame came with Campagnolo dropouts and first generation Super Record. However, they do seem to have made 531 butted frames with Simplex dropouts and gears during this time period.
Top tier frames in my experience have matching front and rear dropouts. Simplex rear dropouts and stamped front dropouts would not be top tier.
I would need to see more detailed pictures of the frame and decals to make any more positive identification.
Hugh Thornton
Cheshire, England
From: Jeffery Pyzyk <jpyzyk@sbcglobal.net> Subject: [CR] Mercier 300? To: classicrendezvous@bikelist.org Date: Tuesday, 8 June, 2010, 19:56
I rode a Mercier in high school and college during the mid to late 1970's. Mine was one of the lower to mid range models made with "LuxTub" tubing. The Mercier got lost in the shuffle once I purchased my first full-campy bike, an Austro Daimler, which I still own and ride today. I have since accumulated way, way too many bikes. Most are Italian, with a few Spanish, American, Austrian, and Mexicans thrown into the mix. I have no French bikes, besides my wife's old Gitane, and my father-in-law's Liberia (which may be Belgian, I don't even know). As such, my knowledge of French bikes is very limited. I have had my one good eye out for a Mercier, mostly for nostalgic reasons. Recently, one came up in nearby Sheboygan (good brats and a Mercier to boot!).
The bike has a Reynolds 531 frame, including the fork tubes. I can't read french, and the sticker is flaked-away, so I can't tell if it says double-butted or not. The rear dropouts are Simplex and appear to be forged. The front dropouts are unmarked and look stamped to my eye. Front and rear dropouts have chromed "socks". The balance of the frame is painted with original white paint and black decals. The bike came with an Ideal 90 saddle with alloy rails, a Stronglight alloy crank, Campagnolo Nuovo Record front and rear (Pat. 73) derailleurs, Campagnolo Nuovo Record shifters and shifter cable guide, Campagnolo Tipo high-flange hubs, Rigida 27" alloy clincher rims, no-name alloy stem and handlebars, and Weinmann center pull brakes.
Is anyone familiar with what model this might be, and if so, whether the parts are original? I would have thought that the bike would have Simplex/Mafac rather than Campy/Weinmann. However, the bike is very original. Dis-assembly revealed fresh, shiny paint under the components.
Sorry I missed Cirque this year. Hopefully I will see you all there next year.
Jeff Pyzyk
Milwaukee, WI