I think that there is very little doubt that this frame is a genuine Jo Routens, whether or not the dynamo bracket is brazed on to the front fork blade.
Both Jo and , later, his son Jean-Paul, developed a very distinctive and readily identifiable type of wrap-over seat stay eye,in which the points of each plate or eye are filed to a very long shaprp point hwich are wrapped over the top of either the seat cluster or the top-tube, with the points just about touching. The cluster on this frame is of that type.
Both Routens had adopted as standard the practice of fitting the rear brake forward of the brake bridge, like the one on this frame. Much as I respected the Routens'...never knowingly met Jo, but know Jean-Paul very well.. I have never been able to understand the logic underlying this particular practice.
The cable routing for the centre-pull brake is 100% Routens.
The bike is not a randonneur, in the meaning of being a touring bike, it is a "cyclosportif".. a fast, stable, lightweight bike, that needs to carry mudguards, probably lights, and at least a handlebar bab. It probably doesn't have pannier rack eyes on the drop-outs.
Cyclosportif activities are the most popular type of cycling activity in France..there are 100s of 1000s of such cyclists in that country. They ride local and regional events as well as events such as the Marmotte, the Louison Bobet, the Ardechois (upwards of 15000 participants last year..over one weekend in June), the Rallye de Vignobles etc etc not forgetting, of course the Paris-Brest, . Cyclosportif bikes are the back-bone of the French lightweight trade.
Bear in mind that Jo Routens worked in Grenoble. Each year there must be at least a score of major cyclosportif -type rides within the immediate vicinity of that city..then of course there are the Alps, the Vercor etc etc.
Jean-Paul still builds, as does Daniel Cattin just about 20kms up the road to Chambery from Grenoble...cyclosportif tandems. It is quite normal for these to use the Mafac centre-pull, as opposed th b/o cantilever, types brakes, with the rear one forward of the bridge.
I had not seen that type of Jo Routens decal before. it looks to be one of those self-adhesive aluminium film type, which was very popular in the 60/70s.
Norris Lockley....Settle UK