Frameset + bottom bracket + headset weight?
 

I weighed the trek 520 frameset with all of the above, and it came to exactly 7lbs. It's a reynolds 501 frame. How does that compare to other stuff, out of curiosity?

501 framesets would not typically get you into weight weenie zone, compared to more lithe tubesets like the 753 or Supervitus 980, but would usually build up to bikes that weigh around the plus/minus 23 pound region, using mid level components, which is really not bad at all, considering the robust nature of 501 frames.
Something like a Brooks saddle would not help in the weight control effort as much as a new nylon or CF based saddle, so you can make a special effort to carefully consider your compnent choices to minimize the weight gains as you build up the bike. and possbily come up with a bike even lighter than most expect with a 501 Reynolds frame.Anyway, I don't think you can consider a classic steel racing/sport bike as "heavy" as long as it does not get too close to 25 pounds and up.
JMOs

Chombi

Good estimate, I was aiming for 22-23lbs. I won't know until the new seat post and saddle arrives :) Pretty light for such a cushy riding frame IMO

Reynolds 531 and full dura ace from the same time period would just barely be under 22 so try to keep yourself grounded.
You also have a significantly more resiliant frame than 531sl or 753.

To get into real weight weenie territory your accumulated figure should be right at 5 lbs

The bike is complete minus the front tire and tube, seat post, and saddle. My hanging scale reads 20.5 and the digital floor scale (- my weight) reads 21 lbs.

It's lighter than I thought it would be, that's for sure. Keep in mind it has 700c wheels and clipless pedals...

I address the weight issue in this feature article on MY "TEN SPEEDS. How Much Does It Weigh?