Well I have some pics of the light (1850g bare) frame I was cleaning up and I'd really like to find out what it is. The frame came to me with an assortment of mismatched and obviously non-original components so they give no clues to the bike, even the age. It was originally painted a pearl white with no sign of decals and, as that seemed to be the original paint, that doesn't bode well for a definitive ID! Dropouts are Shimano and BB shell is Hitachi it would seem, so I am guessing Japanese origin.

Anyway here are the pics (by the way the forks are non original).

Whatever it is, the frame has really nice details and looks very well built. I would love to find a frame like that.

Oh, I forgot to say BB is 68mm British

I wouldn't know what it is, but I wouldn't care. It's obviously nice and it's my favorite color. You're on a roll, dude.

That's a really nice one. 3Rensho?

It does look like a very nice frame. The lugs remind me of Nagasawa.

Looks tight, yo.

it certainly does share some details with that and with some 3Rensho, too...but don't know if it's either since the frame bits I see could be either or none. It's certainly a high-end Japanese frame, the BB shell is investment-cast Hitachi (same company as makes the electronics).
How about some details of the forkcrown? (which does not seem to have the 3Rensho offset, AFAI can tell)


edit: Sorry, didn't realize the fork was not OEM, need to read more carefully.

Fork is not original to the frame.

I'd think them top eyes at the seat cluster would be an identifier. They're some fine details!

unfortunately they are common to many makes, but most of the time the builder's name is engraved in the center...no mystery, then.

Thanks for all the replies so far, I had a feeling that this would be difficult to pin down.

I hoped that someone might recognise the serial number format "M6A00214", maybe someone will.

the serial number IS going to be the best clue, and our resident serial number sleuth (T-Mar) has been inactive, lately. If he sees this he might have some insight, but most of his expertise is with the big factories where this could be from a "boutique" low-output builder. Clearly it's a fine frame, even if it never gets a name.