At long last found the problem. After endless cranking I eventually got fuel dribbling out the injector lines. I tightened them up and nothing. I've gone through glow plug circuit and getting 12v to plugs, bad plugs replaced. I replaced all the return line components and hoses, including O-rings on injectors. Even though I had it running at one point, Something else had to be wrong besides air leakage into the system.
So I pulled the cover on the injection pump. I had done some reading up on this pump and had a general idea what I should be looking for. I visually checked shutoff solenoid, and yes, it was working. I actuated the throttle and saw the governor mechanism doing what it should. But then I noticed that the metering valve didn't seem to do anything. I stuck a small screwdriver in there and discovered that the fuel shut-off mechanism was stuck in the closed position. Even though the solenoid would retract, the following mechanism would just sit there, keeping the fuel shut off. I manually moved it back and forth several times until it was completely loose and would flip forward. The spring that moves it is very weak.
I put the cap back on, and cracked all the injectors and hit the starter: fuel immediately began leaking. Tightened them off, let the glow plugs cycle and it started right away.
What was really screwing me up was the fact that if you grind the starter enough fuel does come out of the injection lines, even with the fuel shut off. I'm experienced with 2 and 4 cylinder marine diesels that send very little fuel to small injectors and thought this little quantity of fuel was normal, especially since everything checked ok. Once I fixed the problem the volume of fuel coming was obviously a hella lot more. Live and learn.
I suspect people who have engines that won't start and suddenly do after a seafoam soak might be having this same problem. In my case, because it never did soak in the pump as I ran it all through, it never had a chance to dissolve the goo that was causing it to stick.