Well, things just kept getting worse, but I think I'm getting somewhere now.
It turns out that I was fighting at least two separate problems, neither of which cause a rich mixture, but one that made it "seem" rich.
As I kept going through the system checks, the issue kept getting worse, until after a short time it would no longer run or start at all. At that point, I moved into checking the basics. I need fuel and spark. Still thinking this was a single fuel issue, I looked into spark first as I figured I could quickly verify that and dismiss it.
Not so. It didn't take long to determine that the points had almost no gap, which caused very retarded ignition and incomplete burn. This was a cause of what I thought was a rich mixture.
I quickly reset the gap, and it coughed once when cranked and that was all. Looked again and there was again no gap.
Turns out the pivot pin on the point set was loose. Points were bad. Installed new points, condenser, cap and rotor. Now have good, consistent spark in all 4 holes. One down.
Still no fire though. Next step was checking for fuel. Plugs were all dry, so I pulled the fuel line from the passenger fuel rail, put it in a cup and switched on the ignition. Heard the pump run its normal 1.5-2 seconds, but no fuel in cup.
That's where I left it last night. I now need to track back to find why no fuel. Looks like the filter before the pump is full, but I haven't gotten under the car to look closely. Pump and all lines are new, so I'm thinking either the in-tank sock has been clogged, or perhaps I've got a kink in the line coming out of the tank.
Won't have a lot of time to look into this today, but will follow up with what I find when I do get back to it.