Nicks neo retro Sunday best. A light for steel stealthy Colnago master x light finished at last

I've just spent £140 on a shiny new Colnago seatpost I'd like to use it and i want to get rid of any corrosion and treat the frame. Hopefully cleaning it up should leave me with 27.2. The tube shouldn't be undersized but I'm going to measure the tube and post before I start doing anything.