Update: after a bit more reading, I deduced that the pin which I had previously thought nothing more than a locating pin for the top cover is actually (also) a retaining pin for the crank shaft. I ground a larger flat onto the side and pulled it out. My previous hammering had bent it, and it wouldn't have pushed through to the other side. The shaft was then easy to remove with tapping. Unfortunately, the shaft or bearings (which are simply holes machined in the cast iron body) have become distorted from my prior attempts at removal, and the shaft is now a very tight fit. I will gradually reduce its diameter with fine sandpaper until it is again fit for service. This is not ideal, but a reasonable solution given the cost of machining a new shaft (assuming only the shaft is at issue). The gears remain in fine shape, and I will not make the mistake of removing the other shafts. The immediate companion shaft (not the rotor shaft) has no apparent retaining pin, but still did not move with my earlier efforts. Yes, I did remove the large gear set screws. The smaller of the two gears (about 1" diameter) on this second shaft has no apparent set screw, and never loosened.
I believe this is a model 40, but it is not marked on the casting.
As a final note, a previous thread from 2010 on this subject is out there, but the tale is mostly told in images whose links are defunct. Very frustrating.
-tap