"This plunger has a shape and fits the cam and also has worn into a specific vertical orientation"
What? I've had my rod out several times, the end is perfectly smooth and polished.
On the lift pump replacement ; Use a dab of grease to retain the rod in position. Its easier to get the rear most bolt started first as it has the worst access. Its the harder one to get in so do it first, doing the front one first can lead you to spend hours trying to get the rear bolt aligned. Just thread it on a few turns..then install fuel fitting and tighten fitting, its almost impossible to do if you do the bolts up first. Then install the forward bolt, lastly tighten the rear bolt. On rear bolt I use a 1/4" ratchet with combination of short socket and extension and just a deep socket. The clearance is very tight, Helps to put some gasket sealer on gasket so it stays in place.