Click here for a brief word about how I came about the monitor placement.

Measure and mark the points of the monitor support.  Draw a line between the two points.  This will be the top of the monitor support.  This is where we had to be inventive.  We did not own clamps that were long enough to hold the boards together while we screwed them together.  To solve this problem, we took a 1/16" bit and predrilled two holes two inches down from this line on this side.  Then we laid the first 16" 2x4 on this line.  Then I got under the ply side and my assistant sat on his knees on the board to keep it from slipping when I drove in the screw.  For the innocent spectators, it was a bit humorous.  For obvious liability reasons, I did not include photos of this.

We measured up 1-3/4" from the bottom of the ply side and placed the bottom edge of the base along this line.  We screwed a couple screws to hold it in place.  We then screwed two screws from above the monitor shelf down into the 2x4 support. 

This held everything together enough for the time being.  Every step we measured to make sure everything was as it should be.  Miscalculations at this point could make the cabinet sit askew or make the monitor sit un-level.  Neither results were what we were looking for.