Best way to test a lift pump? '89 F800 7.8L

The engine on this thing isn't getting any fuel - ran for five minutes, then started loping a bit, nd choked up and died. Ran for another minute or two, then same result, and wouldn't start at all afterwards. I can prime it using the little Bosch primer pump until fuel leaks out of the relief screw, and it'll almost want to start afterwards, but not quite (just a couple of rattles turning over). Is there any way to see if that lift pump's working properly the rest of the time, before I have to start worrying about the main injector pump? The problem is that I'm working by myself, so I can't turn the ignition and watch at the same time.

What I'm looking at:



I do sort of wonder if the shutoff solenoid is stuck, I seriously can't remember if it's supposed to be in that position. But that seems very unlikely.

Also, anyone know what a good replacement would be for a Parker 3-way valve like the one picture would be? There are four on this truck serving various purposes (brake gate & emergency shutoff), and they're almost impossible to find. The few I can find are like $300, which seems absurd for a little valve.

 

Yep, and I'll edit it to reflect that.

Just a bunch of air in the injection lines - one of the charming little quirks of the truck that I'll be fixing over the winter is that if the diesel tank gets much less than half-full, it'll start sucking air. I had to crack and bleed the lines with the manual primer on the lift pump, and make sure the tank is completely full (I discovered this while testing the lift pump).