1981 not getting fuel after replacing intake manifold.
 

So I replaced my intake manifold with an Edelbrock 2101 and replaced the stock Quadrajet carb with a 1406 Edelbrock. When I put the thing back together I couldn't get the car started and its not getting fuel. I've disconnected the fuel line from the outlet of the fuel pump and no fuel there. I've added 7 gallons of fuel to the tank (of note, or at least a clue here is the fuel gauge read full even before adding the fuel).

I had a shop do some work to it before I started replacing stuff (they replaced the shift linkage and rear brakes for me as well as some "AC" work.) I asked them what they thought and they said "Oh, we had the same issue so we pushed fuel through the system boy pressurizing your gas tank." I can say it ran fine after they did that until I ran it out of gas replacing the intake manifold... Not intentionally mind you, the gas just kept coming out even with the battery disconnected (mechanical fuel pump anyway so it shouldn't have mattered). So anyway, I don't have the equipment to pressurize the gas tank. I've tried pulling gas through using a vacuum pump but all I get is some negative pressure that's released when I open the fuel cap. So... what's wrong with it and what can I do?

Welcome to the forum.
My best guess is the fuel pump has gone Tango Uniform. Can you hear the fuel pump prime when you turn the key on?

Fuel pump.
 

Mechanical fuel pump so I'm pretty sure they don't prime that way. Its also pretty rare for them to fail from my understanding.

I read your post too quickly and I see it now. Are you sure that the mechanical fuel pump is still good?

Might try disconnecting the fuel line at both ends and blowing it out.

One of the things I tried was hooking up a vacuum pump on the fuel line coming out of the fuel pump to try and suck fuel through. I can create negative pressure in the tank so I know its a sealed system but no fuel comes out. Given that I'm able to pull air through the line and create a vacuum in the tank I just don't think it could be the fuel pump. That said, I am willing to buy one and change it out if that's what people think the issue is.

I'd still try blowing the line out from the tank towards the fuel pump. The fuel pump does not have much suction power. So just because a vacuum pump can pull a vacuum on the tank, it might still have a restriction that the fuel pump could not overcome.

Would be interested in knowing what you finally come up with to fix it.

Check for a plugged "in line" fuel filter or a collapsed or weak hose.