I have all of the trim in place and it even has the first topcoat of paint. Nail holes are filled and gaps are caulked. All that's left is to sand the wood filler and apply the final topcoat.
I ran into one small snag while installing the head casing. Unfortunately, the windows weren't quite centered on the wall. They are offset by about 1" to the left of center. This meant the lentil for the windows needed to be trimmed asymmetrically. The pictures show how each side mates with the cabinet crown moulding.
To trim the left end of the lentil I made a paper template by tracing the pre-assembled head casing onto regular typing paper. I then put the template in place and cut the paper to an exact fit. Then I put the paper back on the head casing assembly and marked where to cut. I was hoping for a nice snug fit, but my hand-sawing skills are a bit lacking, so I had to fill the gap with caulking. (Please don't tell anyone!)