Originally Posted by
crandress
I am betting mid-60's given the lugs and stem, but could be wrong. I think they have always been fully customizable, so is hard to tell. But interesting the lugs are more simple than most Mercians, even from the late 60's. I may just not see the details in the picture though. Love Mercians.
-----
Am thinking slightly earlier.
Note that 3TTT Gran Prix stem is early hex head expander type.
Dropouts are not Campag 1010, may be Juy, or Cyclo, or Agrati... (not Zeus)
Also note brake reaches and clearances.
Chainstays appear to be rapier pattern but quite slender. Slimmer than those found on bicycles which employed rapiers of the later sixties.
Serial will likely be revealing.
-----