Help! I'm having a fuel problem...I think!

We're stuck and I just don't know where to go for help! I just got a Mercury Comet '63 1/2 S-22 Hardtop.

Here's my problem (please excuse my lack of knowledge!):

It wants to start, it turns over, but there seems to be some sort of fuel problem. We did get it to start right up when we ran fuel directly from a gas can to the fuel pump, but other than that it just won't get fuel.

We drained the gas tank (in case there was something in the fuel), replaced some fuel line, fuel pump and sending unit. Then we used an air compressor to pump air directly through the fuel line under the hood to see if would could feel any air coming out the other end in case it was clogged somewhere. At first we couldn't feel air, then we could. Then we couldn't! We just can't get fuel flow!

We're STUCK! Any ideas?