The pump runs on an eccentric bolted to the end of the cam, so worse case you'd have to pull the timing cover and replace it and not the whole cam.
But I doubt that's your problem. If you installed the pump and felt spring pressure against the pump arm then you're good. What I would try is filling the bowl on the carb with fuel so the engine will run for more than a couple of seconds. Start the engine and give the pump a chance to get fuel up to the carb. Or disconnect the pump outlet and feed it to a container. Start it up and verify that the pump is working - or not. A little cranking alone might not be enough to get it primed.
