TO bearing or clutch disc hub maybe.
The spark plugs - you can hear it lean popping in the first video so it isn't going to lend itself to plug chop tuning until you get that resolved. Might need to have the carbs balanced or have the idle circuit richened up some.

Thanks pampadori. I'm still debating whether I should drive or two to the shop, despite knowing towing is less of a risk.

I had a loose flywheel that sounded very similar (but worse). That dull, inconsistent, clunking sound.
Good Luck.

I guess the noise is trans related and not engine related.
A shop near me, once told me that you can get an irregular clunk in the gears at idle, from a less than smooth idle. If you are able to increase rpm a couple hundred to stabilise, does the clunk go away?

How's your trans fluid level?

Does it clunk when the trans oil is cold? or does it only do it after the fluid warms up?

I've had a car with a similar sound... when cold, it was silent. But when warm/hot, the trans oil thinned and I would get a clunk every so often. Clutch in, no problem. Turns out my idle was not perfectly smooth. Once I got it sorted, the noise is pretty much gone at all temps.

Another test you could try, is coasting with the car in different gears.. engage the gears while the car is rolling but with clutch depressed. ie let the cars forward motion and the rotation of the wheels, drive the gears in the box. See if you have an issue with 1 particular set of gears.

Last year, my car ended up having a broken tooth off 2nd gear; not a dog tooth, but an actual tooth off the 2nd gear itself. Sure the car drove and all, but it was clunky sounding. I drained the oil and found the tooth sitting on the magnet!
Hoping this is not your issue.. But if it has been driven hard in events, you never know?

1) It makes less noise when cold.
2) The noise seems to go away with a little RPM, but it's admittedly hard to hear over the exhaust.
3) I questioned the fluid level as well and will check it. The fluid is only a year old. When I changed it, I added around 3 quarts, which is "less" than the specified capacity but the trans was certainly not accepting more fluid. Car was level.

The idle is certainly a little rough. Car was tuned prior to my ownership and I haven't tinkered with it because it runs very well at RPM.