Yes, the pump arm needs to be pushed downwards as it is being installed. As you described above, sounds like this is not the case. Thankfully, on your application, it's not a difficult fix.

Now, with that said, make certain that there is at least half a tank of fuel, the fuel filter is fresh, and the truck is parked on a level surface, 30-90 seconds of turning the engine over while pouring a little fuel in the carb, or using starter fluid, should pull fuel through the l-o-n-g fuel line from the tank to the carb, and it should fire up and run on it's own.

Before you try, pop the gas cap off, then reinstall, strange, yes, I know, but trust me, it's a Ford truck thing.

Hope you find this helpful.

Bill S.