Here's other Giro D'Italia bikes, Different paint than yours but the same frame details. Yours is very similar to the Pro Model, but it's not. Almost like comparing the Raleigh Professional to a Raleigh Competition. Similar but different. Your frame set was built for Center Pulls, more than likely a mid to late 60's frame set.
http://www.flickr.com/photos/7441811...7623984107578/
http://www.carltoncycles.me.uk/mybikes/66giro.htm
Just finished my 1972 Carlton Pro.
Another Carlton Pro I found On the net, this guy is using 27" wheels on a frame built for 700c.