Brian, it seems that we're all getting these Mercians lately. My finished build thread should be up soon for mine. Same story, small dent in the TT.

Your lugs seem to be more ornate, and I can tell this a later bike because of the braze on FD cable guide. If there's a serial number on your BB or your fork steerer, the last two digits seem to signify the years on these.

Another weird thing: mine has Shimano dropouts. I was stumped why this was on a British bike, but it appears that Mercian pretty much had basic frame guidelines, but the customer could pick and choose almost anything on them.