OK, encouraged by these responses, I have "muscled" the pistol grip onto the lower, and the selector seems to function satisfactorily! We're having fun now!!!
Then I sat here and, well, I don't know how to describe it other than I "fiddled" with the stock for a bit. There is a threaded gizmo, so I turned it back onto the stock and pretty soon, the whole thing popped into submission, and now appears to function as I expected.
Encouraged by these successes, I'm off to the races!
I still haven't figured out how to get the pivot pin back out, but now that I am on this roll, perhaps it is just a matter of more "fiddling".
I imagine you guys who know all about this are laughing your asses off, but the last thing I built was a shoe box when I was in the Cub Scouts, more than 50 years ago! I am doing this as a learning experience, after all! And it's cheaper than buying a California legal already made up equivalent. So I appreciate teh help, alot!