Im going to assume your still running the SU's since its a 71.
If your lines are clear and its not getting to the filter my first guess would be the mechanical pump (also going to have to assume you still have it since you didn't specify) pull the filter cap off and fill it with fuel, put it back on, hook up the lines and see if the mechanical pump will suck it out. You said you tested the pump but by saying its pointed in the right direction Im assuming its an electric to push fuel up to the mechanical (my 73 had one from the factory) since a mechanical only goes on one way.
Do you have fuel in your float bowls? If not, I would pull the tops off and pour some in there to sort of "prime" it. Few more gallons in the tank woulnt hurt either.