Hello all, I snapped this frame up the other day for not a lot but haven't a clue what it is. It arrived this morning and I have had a look at it but am still none the wiser. As there seem to be so many knowledgable people on here I'm hoping someone can help identify it.

Measures:

57cm - centre bb to top of seat tube
56.5cm - top tube
130mm rear spacing
68mm italian threaded bb (unusual? i thought they were meant to be 70mm..)
27mm (maybe 27.2) seat post - it is definitely bigger than 26.8mm at the top and I was told it is 27mm however my cheap plastic ruler isn't really accurate enough to tell.

Front fork dropouts marked columbus, rears appear unstamped.
'B' engraved on the top of the forks. See pics - doesnt look like a bianchi or basso 'b' though.
It has been repainted/coated and I think the original colour was red. Came with a load of rossin stickers on but I know it's not a rossin so they were swiftly removed.

Here's one major dilema...no serial number. Unless the blue powder coating has completely concealed it, there appears to be no serial anywhere. I have looked on the bb, fork steerer, pretty much everywhere. Is there anywhere in particular I should check?

Cheers