It's definitely a frankenbike with the components being of various levels and most older than the frame itself. The Portacatena rear dropout indicates it is no older than 1978.
We can't provide an accurate value without knowing the level/model of the frame. To do this we need to establish the the tubeset. The two best indicators are the set post size and steerer tube.
The seat post will have the size stamped on it, somewhere. Most Campagnolo post are stamped at the on the back, at the top, below below where the saddle mounts. Most other manufacturers stamp the size on the lower section of the post, so you may have to remove the post from the frame to find it. It will be marked something like 26.8, 27.0 or 27.2.
We need to establish whether or not the fork uses a Columbus steerer tube. To do this you can remove the fork from the frame and check the outside of the steer tube for Columbus' dove logo. Alternately, you can remove the front wheel and check inside the bottom of the steerer tube for five helical ridges. They are only 3.5mm wide and and 0.35mm thick and often obscured by road grime or rust, so use a good light. I'm attaching a picture of what you are looking for.
Also, are there threaded holes for a 2nd water bottle cage of the seat tube?