Sounds a reasonable deal to me.
I'm 5' 10" and it would be too big for me but i've got short legs for the height - best thing to do is go and try it if its nearby.
The bike is probably early 80s with a 6 speed block. At the time Dawes weren't the best off the shelf bike (at the risk of mass disagreemnt imo that was Holdsworth, by a country mile) but they were good, fairly high end, bikes. The frame should be in good nick (barring any accidents in the past) and a small amount of non penetrating rust shouldn't affect it. treat it if you buy it.
I've done work on bikes of that age (since they were young!) and would just comment:
Original spec components will be a problem, and modification for current ones, though fairly easy, is time consuming and fiddly.
The wheels won't last forever, and you may want to fit current ones. The rear dropouts will need widening, and that's the nastiest job I've ever done on an older bike. There are several descriptions on this forum.
If the freewheel block fails you may find replacing it difficult - again you could be into new wheels.
I have toured France several times, on bikes made in 1967 onwards, and down to 5 gears. Provided you don't mind a wider cadence range than is now usual (ever ridden a single speed?) and the gear range is wide enough then you should be OK with the 12 speed.
The last time I was in France there were still plenty of bike shops, and past experience has been that they keep all sorts of stuff of all sorts of ages. Nonetheless it would concern me being on a bike that old.