Success!
I spent another hour crouched over my engine yesterday, with very satisfactory results. With minimal effort, the shaft slid out of the coupling, and I pulled it out of the stern tube. Whew! The water-proof grease applied to the shaft during reassembly two years ago really paid off.
I slipped the first spacer between the halves and easily pushed the shaft out of the coupling 3/8 of an inch, as I pulled down all four bolts in sequence. After loosening the bolts and backing off the coupling with the additional space provided by 3/8 inch, I slipped a longer spacer between the halves. I only needed to tightened one of the bolts this time, as the shaft easily pushed out of the coupling. Still too tight to free without a bolt and nut to draw them together, I used one more (longer) spacer to push the shaft towards the end of the coupling. At this point, I was able separate the shaft and coupling by pulling back on the prop from the outside.
Additionally, I was able to reposition myself more comfortably over the engine, so wasn’t crippled when I straightened up.
Photographic evidence of successful removal follows below.
Ready for the last spacer to push the shaft out to the end.
And here’s the assembly – photo taken outside the machine shop.
middlebaysailing 
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Shaft work is such an annoyance. That’s probably why, when I was working in a boatyard, so many people hired us to do the work for them. Some engine compartments are so tight. I think the manufacturers don’t really put much thought into doing that work after years of salt water exposure. Still, it’s less work than yanking the engine out!
Good luck with the rest of the project!
Yes, absolutely better than pulling the engine just to get the shaft out. Actually, other than the posture necessary, it wasn’t bad this time. Hurray for water-proof grease!
YES!