Originally Posted by
unterhausen
the one the OP mentions is a really nice bike. Nicer than most of the inexpensive 650b bikes available now. It's not some historical footnote.
For perspective the Motobecane Grand Jubilee and Grand Record were a popular choices for experienced club cyclists looking for the "high-end" long distance machine > 40 years ago. Famed for a compliant yet efficient ride quality, full 531 tubing, beautiful finish and a well though out component group they rivaled the Schwinn P-10 Paramount and Raleigh International as the trick-setup(s) for fast century + rides and overnight club events "back when".
Nothing about that ride quality has changed, unless abused/crashed, in the last decades.
Try to find a "modern" frameset with
that quality, perhaps what BQ refers to as "planing", these days with over-built "gravel" and "touring" on offer not light/fast/compliant steel designs.
Doing a full-on "modern" retro-fit regardless of wheel size choice requires a frameset in
exactly the right size in great condition, tight/specific requirements planning, a good sized budget, considerable C&V knowledge, good mechanical skills, competent frame spacing/torch work, a good finish shop and a considerable time-line. The result can be a particularly suitable LD machine with idiosyncratic character or a horrid/expensive/kludge. One or the other.
-Bandera