Can anyone help me with this? I've got an un-named frame. The serial number is M0E21307 which I think makes it a Miki frame from 1980. It has been built into a single speed so there is virtually no original equipment left on it apart from the stem and seat tube. The seat tube is an SR Laprade marked Japan 26.4. The stem is also marker SR. The brake levers are Shimano. The chromed fork suggests a slightly higher end model. The fork steerer tube is marked Tange OD and has traces of gold or tan paint, a similar colour to the 2700 GTs I've seen.

From looking at the few pictures I can find, The only model I can find with identical lugs is a 1979 Sekai 2700. I know Miki made frames for a few brands so this might not be a Sekai at all, but I can't find anything else with the same fork crown and lug arrangement. I bought it in London, so maybe it's more likely to be a European brand but I've looked at the likes of Union Sakai and they tend to have a different fork crown with a sharp point in the middle instead of a smooth scoop.

So my questions are, is there any way to identify this firmly as a Sekai?

Does the seat tube dimension give any clue as to the tubeset?

Thanks guys.