Thanks for the website tip.
Now, after further thinking, seems like I should be able to just:
1. Line up the flywheels to the timing mark.
2. Line up the breather hole on the pump.
3. "Mark" the bottom of the pump housing to line up with the key.
4. Slap in the pump, manipulating the gear to end up in sync with the markings.
Any problem with this plan?