Good point, if you had the blunt end down, I suppose it could resist dropping into the pump, but still, I've always held the distributer down with a bit of pressure, had someone bump the key and it practically falls in by itself. I'd pull the distributer, the oil pump drive shaft and have a look down there to see what's up. With a decent light you can see all the way to the pump, make sure some bit of crap hasn't fallen into the shaft hole. Also, whoever built your motor is at fault, when the pump is bolted on, there's supposed to be a little one-way clip that slides on the shaft, then the pump and shaft are bolted on and the clip should be close enough to the block to prevent the shaft from coming out with the distributer, of course it should still go together easily, so be patient and rather than fight it, keep looking for the reason it won't go, you'll get it.