This seems to be the place to go to see if anybody has a nice steel Colnago decor frame for sale. Gilco tubing preferred. Size 57cm, (give or take a little)
If I remember rightly the sizing was in the .5mm so a 57ct would have had a 55.5 top tube and a 58 would have had a 56.5 tt [colnago used to have the exact geometries on their website.
New (old) Kona fire mountain