It's definitely a steel frame. The attributes indicate mid to late 1980s and almost certainly Columbus SL grade or better. However, if you want to be sure, ask the seller to verify the presence of helical ridges inside the bottom of the fork's steerer tube. The bottom bracket, crank arms and headset are going to add close to 2 lbs, so the weight is in the ballaprk for a Columbus SL frame and fork of that size.