Thanks for the tips!
I don't have a compression tester. This is probably where I should start. I've seen several posts regarding the kit from Harbor Freight, I think, so I'll get one coming.
In a gas engine, one can drop some oil down the spark plug hole and test it that way as well. What's the best method for the diesel? Same thing, but down the glow plug hole? Or not at all?
I beileve the clunk is the starter pinion engaging the flywheel, and giving it its all, but it isn't enough. The fan blade can be seen to budge, but only an inch or two, and then when the key is released, returns to where it was. There isn't enough torque available to turn it over, but it isn't absolutely clear whether there isn't enough available, or whether what's required by the engine is more than it should be.
When I had the lines off to pull the injectors, three of them had fuel in them, but one did not.
I haven't tried cranking with the lines loose, so I'll give that a try.