After several weeks' hiatus, I spent all morning in the shop today. A test fit of the neck showed that the angles were pretty good, but the base wasn't seating properly on the tongue. A bit of careful sanding brought it into alignment. I also cleaned up the mortise, partiularly the large flat, to make it as consistent as possible.
Once I was satisfied with the fit, I mixed up a new batch of hide glue, with a fairly thick consistency. I used two small clamps so that I could set the alignment gauge between them for a final check on the angle.
The entire assembly is now sitting in the holder, where it will remain for a couple of weeks until I am next open to spend another day in the shop. The glue will certainly be properly set by then!