Originally Posted by T-Mar

The cinch slot for the seat post is notably pinched at the top, as if a previous owner used an undersize post. Gently pry the cinch slot open with a large, flat bladed screwdriver, until it is slightly wider at the top than the bottom. Also, make sure there are no burrs or foreign material build-up on the inside of the seat tube. If so, remove with a reamer, hone or emery cloth. Then try your 27.2mm post.

Did you remove the fork? The Columbus dove logo is the outside of the fork's steerer tube, so you have to remove the fork to see it. Sometimes it can be quite faint. You can also verify a Columbus steerer tube by the five helical ridges on the bottom inside of the steerer tube (see attached). On old frames like these, corrosion and dirt build-up can make them hard to see.