SJX426 

Pictures would be of great help, maybe, in dating based on the graphics and frame construction. Include drive train on both sides and the rear triangle to get a "picture" of your brake configuration.

SN may be hit or miss. I have a 1972 Motobecane Le Champion without any SN. I know it is a 72 from the color, configuration of components and the fact I bought it when it was a year old! But there are other features that can help in identification of era. The Mafac's are a good indicaiton of it being in the 1970's range.

Do a google search on 1020 vs 2040 framed bicycles. There is a wealth of info out there.

I am new to Tandems so don't know the timeline for construction geometry but ..... there have been changes in the rear spacing of the drop outs. You should measure it for us. it is the distance between the inside of the drop outs with the wheel installed or the distance between the nuts of the wheel (those that mount on the inside of the drop outs). This will help determine the significance of changes you are curios about. You can likely change to index but to how many speeds will be determined by how much if any adjustment is required to the frame drop out distance. If a change is required, new hubs will likely be needed.

Double pull for the brakes is attainable. Visit Tandem East site or other tandem stores on line for configuration options.

You have a French bike. Nearly all the dimensions are unique to them, as you have discovered with the post. One option is to find one that is close but over sized, with enough wall thickness, it can be turned down to the right diameter. Otherwise you will need to keep searching.

Also useful would be to know your crotch bone to floor (bare foot) measurement and then measure from the Captains crank spindle center to the center or top of the top tube at the interseciton of seat tube. My suspicion is the frame may be too small for you. Do the same for your Stoker and let us know.

Looks like homework, huh!

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