No Start After Rebuild

So, I want to start by saying this is my first vehicle engine rebuild. I've rebuilt plenty of small engines and studied and patiently rebuild my 4g64 with all the care I could muster but I will admit that I could've messed something up somewhere along the line.
So, engine will turn over but not start. The engine came from a 1996 with a bad frame. It would start and run (poorly) before removal. Rebuilt it and placed it in a 1993 frame and body. The engine will turn over, but that seems to be it. It also seems like the battery wears down while trying to start it, but voltage reads fine and if I take the same battery and place it in my f150, it starts fine. I think this might be lackluster grounds on the starter or it may be worn and overheating quicker than it should.
Haven't checked voltage at plug wires, but they are generating a spark. No filter or other potential blockages in intake.
I'm pretty sure the problem is in the fuel system somewhere. I took the plug from the old harness and rigged some wire to run the fuel pump straight to the battery. Still wouldn't start. Oddly enough, after trying with the pump plugged in then unhooking it, it would try to fire, putter a very small but and either die or backfire. I then though this may have been a pressure issue or electrical issue.
I've switched the relay and ecu in the passenger side kick panel for the one that ran the engine before rebuild with no change. I then started testing voltages in wires between the kick panel and fuel pump and only get about .2v on the wires running to the fuel pump. Changed it and same thing. I straight wire this pump to the battery but in now seems to ground out. Both wires spark when connected to the battery and even when touching negative wire to positive terminal it sparks even without the positive wire completing the circuit.

I am sorry for the wall of text, but unless I've missed something, this should be my entire story and hope somebody has an idea. Thanks in advance!

Do the basics first. Check all the ground leads from the frame to chassis and engine and disconnect/thoroughly clean them. If you are getting spark then shooting aerostart etc into the throttle body should get it to fire. If it fires up then your conclusion to the fuel pump being a symptom of the no run situation is on the right track. I would now go through and check the wiring harness from the ECU to the fuel pump looking for damage and check fuses as well.

As far as the wireing for the fuel pump goes, do you know when and what they should read? From the main relay, the wires show .2v at all times. I did switch it with the one from the old truck when it ran with the same outcome, so I don't think it is the relay. Maybe a problem upstream somewhere. I did wire the main relay to the pump using spare wire to rule out a broken wire in the harness at least from the relay back.

Hey I'm no 4G64 expert but just throwing this out there,
Have you verified the cam timing and ignition timing?