I'm going to go out and try to rig up a container with a hose in the cab so it's higher then the motor to feed fuel to the supply line and see if I can get the air out of the lines to just get it going.
Well rigging up a temp tank will answer the question of possible plugged suction line in the fuel tank. Often the best way to figure problems out like this is to eliminate the simple things first. These Detroits are usually not hard to restart after running out of fuel.
Just a quick description of how the standard fuel system should be connected:
One line from fuel tank suction tube to primary fuel filter. Then one line from the primary fuel filter to the suction side of fuel pump mounted on front of governor housing. Next one line from fuel pump outlet to inlet of secondary fuel filter housing. Then two lines from outlet of secondary filter one going to right head and one going to left head. (NOTE some engines have only one on outlet of secondary filter that goes to a tee on one head and a jumper over to the other head.) The last on a V engine is a jumper between the heads with one end of it connected to a TEE fitting that also has a line going back to the fuel tank for the return. This TEE will be stamped with something like R70 as it is the restriction fitting that controls fuel pressure.
It may be possible that this restriction fitting is plugged and causing the problem getting air out of system.
Trying to think of things you could check easy. Any chance you have a small electric fuel pump? Or even a garden sprayer you could use to push fuel into the inlet of the secondary filter. That would be one way to be sure you had fuel getting to the injectors. Pressure is not real critical, for starting, as the injectors create the injection pressure and only need a supply of fuel to work with.
You could have a weak fuel pump or bad seals that would make it hard to pick-up it's prime, but if it ran OK a couple days ago it should run again!
Keep letting us know what you do and what the results are and we should be able to get it running again! I could come up with many things to suggest but best to try one or two things before getting to involved and confused!