Crank, no start, not air?

Hi all. Lurked a bunch to troubleshoot so far. I have a 1997 E300 diesel that doesn't seem to be enabling fuel to start (fuel is going through the LP pump and seems to drip out the return line but there's not even a sputter after extended cranking).

Problem started suddenly, like air in the lines. But I don't think anymore that it's an air issue. Problem persists even running with the rubber lines removed from the firewall connectors and immersed in a canister of diesel where the washer bottle would sit.

Replaced crank position sensor and shutoff valve and its o-ring.

Minimal air visible in lines except before the prefilter. Other lines are full of fuel.

Glow plug light does come on, then turns off after a few seconds and stays off, like normal. No hesitation cranking. Just cranks eternally like it's not getting fuel.

No red/green flashing immobilizer lights on rearview mirror.

No response when spraying WD-40 into the intake manifold with the crossover pipe removed.

Have a new K40 to try, but the symptoms don't seem right.

I'm like...99.9% sure this isn't gas in the tank? Which is what PudgyGuy decided was his problem when he was in this same situation with a '97 and couldn't get it started, and decided to give up. It really was running the same as it ever did, right up until I tried to start it after it had been sitting nose-up for a few days.

What would you do? Is there a diagnostic reader that could tell me if, for example, the non-start is related to the glow plug relay not communicating right? Or am I stuck getting this thing towed to a shop, and then having them tell me my IFI is fried and I have to use my last free AAA tow to get it out of there?