Alright,

So I got another PMD and still same symptoms. Because the truck starts for a brief second or two, I gotta believe the IP is making enough pressure. I tried starting with the advance solenoid unplugged and it was still a no-go. I'm on to the optical sensor now. I have no reason to suspect it other than the fact that I don't know where else to go. I'm going to try removing and cleaning it and see where that gets me.

One thing I noticed is that while cranking with the return line disconnected, I'm not getting much if any fuel out of it. Should I be getting fuel out of the return line, even without the engine running?

 

Any update?

 

I guess I should close the chapter.

I pulled the optical sensor out and it was all clean and the bowl was full of fuel. Reassembled and still a no-go. I finally decided to change the IP because by this point, it was likely the culprit. I think the fuel solenoid (the one in the center of the distributor, not the shut off solenoid) was the culprit as it seemed to have good pressure and there were no obvious failures. I ordered a used one off of eBay and swapped it out. All in all a very simple and straightforward process for a capable mechanic. With the new IP the truck cranked and cranked and I thought it was all for nothing. Then it finally roared to life and ran like a top.

Turns out the IP was the issue all along. Like I said before, I'm fairly certain it was the fuel solenoid.

I hope this can help someone else out with their troubleshooting.