Finally got the old tractor running yesterday, and so far, it looks good.
I was losing prime and it would run out of fuel.
Finally, I pulled the fuel lines at the injectors and cranked the engine until all three lines were consistently feeding pure diesel. When I reconnected the lines, it started right up and I let it run for half an hour. No hiccups, it ran fine.
The real test comes in a couple minutes. As soon as I click "Post" I'm going out to use the old tractor to actually do some work.