Some neighbors down the street had minor stone work done in their yards, and I thought it looked good, so I asked who did their work. Geronimo Casabon. So I called him, and he said he could do the stone work for the top of the wall.
The first problem was that the wall was not quite high enough. So he added 3 to 4 inches of concrete to the top. He drilled into the part that was already poured and then add a small amount of re-bar, to reinforce the concrete.
and then they added concrete on top of the existing wall. It took 4 bags of concrete to go the entire way (and they may have extended it by adding in just mortar mix.)
The objective was to be 8.5 inches below the string. The stones were 8x4, and they wanted to leave only 1/2 inch for the mortar.
This was allowed to dry for a couple of hours, until early afternoon. Then they came back and proceeded to lay the stones in place. A taut string gave height and horizontal position. This took 4 bags of mortar mix. They started at one end, and then at the other end, working towards the middle. They ended up with one stone sliding into the middle, exactly using up all the stones I had.
Once everything was mortared in place, they went back over the stones and the mortar with a brush, to clean it all up.
Excellent work. Well worth the $500 I paid for it.