OK folk, it runs! The answer is a two parter. One involves extreme ineptitude on my part, and one is simple, once you know it, but it took me all this time to figure it you. The first part involves the new key switch I installed (owner had it on the shelf, but not installed, because the old switch basically wanted to rotate every time you turned the key. When I installed it, I mistakenly swapped the two leads to the glow plug indicator (really short leads) where they connected to the key switch terminals. As I was further tracing wires today I realized this and reconnected them to the correct terminals. Tested the glow plug indicator (the original one) and although I could not see it glowing in the bright sunlight, I have a small brand on my fingertip now. So I though was golden at that point.
Gave her a good s l o w 30 count while glowing and cranked. And cranked. And cranked. And bled, and bled. And re-glowed, etc. NO JOY. The GP's were definitely working, because I could see slight smoke trails at each GP, which were hot enough to vaporize some of the liquid fuel sitting there from bleeding. I was totally bummed and pretty much wanted to give up. Meanwhile the owner's wife had come out while I was working and I had no good news for her. She went on about her business and left on an errand. A little while later, I just randomly looked at the compression release mechanism. As I noted originally, the cable was broken (at the knob end) when I started this journey, but I had verified many times that it would crank significantly faster when I operated the mechanism by hand, so I figured it was working correctly. What I did not realize was that even though the mechanism had a lot of travel, and even though the crank speed was way different, The end of the cable still attached to the mechanism was restricting the last bit of travel for the mechanism! So I got in there and freed up the cable and got that last bit of travel out of the mechanism, and gave it a bump.
Right away, just from that small bump, I could tell it was cranking WITH COMPRESSION now. Totally different crank. I knew I was on to it then. So I gave her another 30 second glow, cranked her and she started right up! I let out a yell, I wanna tell you. The neighbors probably wondered what was up. The thing is, I had no experience with this tractor, so I had no idea what the "normal" crank was. As soon as I heard that totally different crank, well, you know. And yes, I know some of you asked me to post a vid while cranking, but yadda yadda, no excuse. So consider this one solved, and thanks to all of you for hanging in there with me. I'll do an oil change and fan belt change next weekend for the woman, and that machine will be good to go.