Hi guys, so I've tried measuring the tubes. Can't be sure with the figures but I hope it might be quite accurate.

seatpost: 26,2 mm, but it seems there is wrong size mounted, it does not fit well, the bolt must be pretty tightened to hold, I suppose the right diameter must be at least 0,2 - 0,4 mm bigger, I'm sorry about that, can't measure it any more accurate

top tube: 25,4 mm
seat tube same size as down tube: 28,6 mm

The BB is labeled SUGINO 35XP1 MADE IN JAPAN, so it is the French size, but it fits weirdly as well...there might have been different one before. There is nothing embossed on the bottom of the BB shell, there is not even a hole. I see I could have really bought a better bike, looks like some crazy many times changed compound