Jeff!
I don't remember whether you have the steel or fiber gear but the #1 knock
candidate is usually the attachment between the fiber gear and its steel hub.
In response to the other points,
1: No way, if you really torqued the nut. The gear should be tight against
the spacer and nothing behind would keep that from happening.
2: Only if you pulled the lifters, and then VERY doubtful if the valves are
opening and closing properly.
3: Again, this is only likely if one or more valves are not opening and closing
properly.
4. I have had this happen and the principal symptom is erratic ignition timing,
NOT noise. The slotted ring on the top of the gear cracks loose on one side
but the other side pretty much keeps it turning.

Other possibilities: If your fuel pump is not bolted up tightly it could
be knocking against the side of the block (and dribbling lots of oil!) Or it
could be coming apart inside and making noise.
I have had a carburetor come loose on its 4 mounting bolts and bang against
the manifold flange. The engine ran surprisingly well at the time because
when the engine sucked it held it on tight.
I have also had soft motor mounts allow the pan to knock against the frame
crossmember - I replaced $1000 worth of suspension and brake parts before I
found that one! Finally if your oil pressure has been very low you might have
a bad rod or wrist pin bearing - serious problem!

Recommendation: If/when you pull the timing cover, be sure and take off the
oil nozzle and make sure the tiny hole just under the head is open. A banjo
5th string or a guitar 1st string works pretty well to rod it out. Back edge
should be parallel to the edge of the gasket on reinstallation.
--
George Downs Bartlesville, Heart of the USA!