#2: The oil pump just barely engages with the distributor. Therefore, it is easy to not go deep enough.
#3: Remove distributor. Position distributor housing where you want it. The housing defines where number 1 is on the cap, turn the rotor to point at number 1. The new cap has numbers assigned on the plug wires. Using a long narrow slotted screwdriver turn the oil pump's slot to match your new location of housing and rotor.
After that, loosen the clamp screws (but, I did a trial without the clamp to make sure that the O-ring on the distributor is not visible, then I did it for real with the clamp, obscuring the view of the O-ring on its way in. You can't actually do anything without installing the clamp first, other than feeling out how to seat it in the oil pump.
Turn the rotor of the distributor 30 degrees (I said 15 degrees earlier, but I was going from memory, not the manual) counter-clockwise to number 1 on the cap.
Insert the distributor watching the rotor turn 30 clockwise as the distributor is being inserted against the camshaft gear, if the gears mesh about correct, then the tang of the distributor will go into the oil pump slot, if it doesn't, then the oil pump gets no spin from the distributor, the distributor will sit high, and you will have no oil pressure.
Make sure that the rotor is pointing to number 1 on the cap.
Make sure that the distributor is seated deeply enough.
Tighten the clamp on the block, and loosely on the distributor-so that you can precisely time the motor to the ball on the flywheel, and check for oil pressure, immediately.