Hmmm. I have the same problem. Fresh rebuild, edelbrock intake, Holley 4175 (quadrajet replacement) ... If I start it every day, fires up no problem. Wait a week before starting and ... Pump-Pump-crank-crank-crank-pump-pump-pump-crank-crank-crank ... etc. I know there is plenty of fuel in the bowl, because the last few times, before starting, I popped the hood and manually operated the throttle. Squirters squirt fuel. There is a clear external fuel filter and, as far as I can tell, the fuel is draining back through the (new) mechanical fuel pump. If the filter is full of fuel, truck starts right up. If filter is mostly empty, it takes several attempts to start.
I used to have a 69 Chevelle with a built 35o, Weiand intake and Holley double pumper. That thing could sit for 6 months and it would fire up on the second cranking revolution every time (in fact, my father-in-law used to brag to people about it).