Need help, what is this. Only marks on the frame are BCM on the head, lugs no braise on's No serial #, no decals, original paint. Campy seat post, crank, headset, & nuvo recoard rear derailleur, modolo flash brakes, suntour superb front derailleur, avocet front hub, super champion front rim, 0 cross lace pattern.

any idea of the seat post diameter or bottom bracket threading?

Any serial number? Indication of it once having a head badge?

BCM = bocama lugs. That really doesn't help at all; neither does the parts mix. The headset and bottom bracket are the last to be replaced, usually, so if these are Campagnolo, the bike may very well have been originally equipped with campy stuff. pretty gentle, non-racing geometry (judging from the long rear stays). I'd guess English, from the semi-wrap seat stays. I couldn't get closer without some pretty solid evidence, though.