Great try! I'm doing this exercise myself. I got frustrated in one of my gesture drawing sessions because the face wasn't automatic for me. So, I have determined to draw enough eye + nose + mouth to auto-magically draw the head really well.

Looking good! I’ve noticed that there’s a pattern where the noses are a little longer (vertically) than they should be. You can check by measuring the vertical distance between the eyes and the bottom of the nose. It’s more noticeable in the last two faces, but the third one kind of has this issue as well.

You seem to have a reasonable understanding of how to get things to feel 3d. You probably can make a pretty good box. But I'm wondering how much were you looking at the reference? I have a feeling you were looking at it a bit too much. How confident would you be drawing these again without/very little use of the references?