I can't really speak to the Dawes but I would love to stumble across a
Grand Jubliee especially in good condition that was my size! A couple
thoughts on "weird French sizing" -a valid concern but......
Motobecane was an early adopter of Japanese parts on their bikes so
depending on the year of the bike the sizing issue may be non-existent
and even if it is French the problems are not impossible to overcome,
bottom brackets are readily available, stems can be sanded down to fit
etc. Based on catalog scans it looks like Motobecanes had Suntour
parts as early as 1976. Also if you ever did decide to sell I think,
based on observing CL and Ebay, that you could get your money back on
the Grand Jubilee especially if the frameset is, as you state, in
fantastic shape.
The Moto GB would make a sweet ride.
Good luck and if you do decide to go the French route I would be glad
to send you some links I have found helpful in working on the four
Peugeot's and one MB that have entered my garage over the last 9
months.
Ryan "admittedly biased towards sweet French road bikes" Surface