Pumps can fail, though the timing is suspect. Is there oil in the pulse line - possibly from being inverted?

the fuel pump is operated by pulses from the crankcase. check the pulse line to the pump.
Also check integrity of valve cover gaskets, dip stick o ring, - anything that would permit the lost of crankcase vacuum pulses.

chances are, the fuel line to the fuel tank was disconnected to facilitate the maintenance. When reconnecting the fuel line, make sure the inner tube on the fuel hose did not collapse - blocking fuel flow.