Ford 3600 playing hard to get

So this is probably my first tractor to have done this on, but not my first rodeo. I overhauled a ford 3600 two weeks ago, everything went well, and I've got everything back together but, now it won't start.
This is New pistons, rings, rods 'n mains, and lapped all the valves. It's a three cylinder diesel btw. So we have oil pressure while it cranks, fuel is getting to the injectors and atomizing pretty well. I had trouble finding timing marks so I ran the overhead twice.
At this point I am almost defeated.. I thought the injection pump might have been out of time but marks are where they are supposed to be. I'm thinking now it is a compression issue as ether is used during crank with little to no effect BUT, with that said, using ether during crank it sounds like its trying to fire and I managed to get it running a whole four seconds before it died, sounding extremely weak.

I need help with any ideas or thoughts; maybe I've skipped over something or possibly some sort of ritual I'm not doing. Either way I'd like to hear what the people think about it. been working on this thing all last week and absolutely need to get it out of the shop. Thanks in advance everyone!

I would bet that you have the injection pump timed 180 degrees out. I have done that a time or two and some tractors will run while others will not. Slide the injection pump back and turn the motor 180 degrees and reinstall the injection pump.

I had the same trouble with a 3910 had the wrong compression rings next time I install new pistons and rings I'll check the end gap before putting pistons in block

JD Seller: The pump hasn't been moved since it has came in. The owner said it wasn't used very often between three or four month periods. Head gasket blew so before I tore it apart I didn't even check if it would run. We have replaced the older diesel, new filters.

D&C Farm: This sounds like it might be the issue. I think about having lapped the valves and perhaps not doing it properly; a combination of things. Might have a comp gauge somewhere but no way to attach it. Would there be evidence of this in the oil pan?

Those 3-cylinder Fords are very fussy about having
ANY air in the fuel lines. It wouldn't hurt to try
bleeding the lines at the injectors again.

I'd definitely do a compression check, see what you've got. Injection pump can't be installed wrong IF the gear pin is in the drive hub slot, AND gear is where it belongs. Can't be installed 1/2 turn off because of the three drive gear bolts. I wonder if the installed piston are the right compression height, if a bit short that will quickly drop compression heat needed for easy starting.

If you got the crank, cam, idler, and pump gears all timed up properly it's nearly impossible to get the timing off. Look at the mark on the pumps mounting tap to make sure it lines up with the zero mark on the mounting plate.
These engines are bad about having the injectors air lock, don't know why, most times after a rebuild I've have to fire them off on ether a few times before it would run on it's own.
Are you sure your getting a good supply of fuel to the pump?

Wasn't able to post yesterday so here is everything that I've done. Removed injectors cleaned and replaced copper washers. while doing so I ran a compression check nothing fancy but a gauge on a stick. Reaching good compression, fuel is flowing. I can't say how much as I can't gauge it but I managed to connect the fuel hoses to all three injectors outside of engine and watch them fire off, all three produce a nice puffy cloud of diesel.

I feel like I messed up setting the valves. When I crank it with my hand over the intake I feel a strong suction but some blowback. I found an old manual for it thankfully. There are marks on the flywheel, up to thirty in intervals of two. I am assuming the '0' mark is tdc? It's difficult to turn it and watch the flywheel so I may have missed a tdc specific mark. anyway I'll check this in tomarrow before I set the valves to be sure. Book just calls it a 'timing mark'

I double checked the systems everyone has mentioned and even found a couple things that needed tweaking so thank you much for the thoughts.