Thank you Boscoe for your prompt and to-the-point reply.
I would also note that to separate the lower unit from the exhaust housing, the jam nut must be removed. Thereafter, when reinstalling the lower unit, I tried to screw the jam nut on to the same place it had been.
That didn't work; nor did moving the nuts around to either side of where they had been.
So, here is what I did which results in it able to shift into reverse (and F and N):
I disconnected the shift cable from the shift lever, and screwed out the connecting attachment at the cotter pin. This lengthened the "throw" of the shift cable into reverse. And seems to have solved the problem, pending further test drive tomorrow.
Did not expect this to be the path to success. Unless you call it a bad solution?