This will be late 50's to early 60's. There's no mention of the Don Juan in the 55/56 catalogue, but the 5 speed gear lever has the plastic 'Dawes' cover which I'm pretty sure was used through the 50's until the mid 60's. I would say the calipers are replacements, Dawes used the 'Talon' calipers on most of their models. You may get something of the crank especially if its a Williams, but all early Dawes are notoriously difficult to date exactly as there are no frame number records.
What make derailleur does it have on?
Fortunately, I have a Dalesman that's dated exactly but I'm currently selling! The previous owner got it for his 21st birthday in 1961
http://www.ebay.co.uk/itm/251061420302? ... 1555.l2649
General cycling advice ( NOT technical ! )
Just spotted the Dawes Don Juan requests for information. ( A bit late for a reply) I had one of these bought new 1956 from Eddie Mcgratth in Urmston, Manchester at a cost of £27. I had to find half the cost of the bike by saving pocket money & doing jobs etc. The frame was a strange shade of yellow & had pale green mudguards-sounds horrible but I loved it at the time. Its big atraction for me were the Campagnolo Gran sport gears which were superb & far better than the usual Simplex or Benelux fitted to other makes. It had GB Sport brakes, Norton Chainset & GB bars. The frame was made from Forte tubing. The bike took me on tours of North & mid Wales, Peak District & Southern Ireland. I rode the bike for some 15 years by which time it was starting to look a bit tired despite several major overhalls. Some kind person took a fancy to the bike cut through the chain locking it to some railings & rode into the distance. Edwarda7
Bought a Dawes Dalesman in 1962 but wanted the Don Juan as it had campagnola gears but could not afford it so had to settle for the Dalesman with Hurett gears and side pull Weimar brakes. My mate had one and I always envied him but for some reason it had Beniluk gears?