Need help: noisy engine after over-rev Options

[DC_neun_vierzehn]

First, it's a '73 2.0 (2056 rebuild with about 1,000 miles on it). 123 dizzy. Car was driving great. No issues.

Then, last November, I over-rev'd my engine twice. First time due to forgetting to put the throttle body spring back on after reinstalling a new gasket under the TB. The second over-rev was immediately after because unbeknownst to me the throttle cable was tangled in at the pedal cluster due to omission of spring. Both times, I pulled the key out IMMEDIATELY, but not before I saw the tach needle shoot WELL past the red line. Both times my heart sank. Still beating myself up for the gaffes. Also frustrated that the rev limiter in my 123 dizzy settings didn't prevent the over-revving. Ed at 123 (great guy) said that rev limiter does not prevent the RPMs from going above the threshold it's set at, rather it prevents sustained RPMs beyond the limit. Ugggg.

First thing I did was look for leaks under motor, in the engine bay, check for any funny smells. Didn't see or smell anything. Next thing I did was take it for a nice and easy drive around the block. Drove fine, but I thought it sounded a little noisy. Next thing I did was take it for a slightly longer drive and slightly less nice and easy. Did not notice any loss of power or any difference it how it drove - just a little noisy. The best I can describe the sound it "loose" (thumpy ... chattery ... a little like a diesel engine).

Then winter came (snow, salty roads, etc.) and I put the car away for the winter and planned to dive in when spring came. For last several weeks, I've been diving in trying to find the culprit.

Here's what I've done so far.

1. Compression tested each cylinder. 3 were at 130. C4 was at 120.

2. Removed both valve covers. Inspected all rocker arms and springs. Everything looked fine. Checked valve lash. C1 and C2 both were in spec (.008 exhaust and .006 intake). However, C3 had .004 for both exhaust and intake, and C4 had .002 for exhaust and .009 for intake. I removed those rocker arms to inspect closer. Everything looked fine. Reinstalled the rocker arms and adjusted the valve lash to spec (matching C1 and C2).

3. Changed oil. Inspected all of the oil visually in a glass jar. Did not see any debris. I ran a magnet through each jar, no metal shavings or pieces on the magnet. I'm going to cut the oil filter open with tin snips later today to see if I see anything in there. Topped her off with 3.5 quarts of fresh oil and new filter.

4. Took a 10 mile test drive. Noises are still there. Uggggg.

5. Removed valve covers. Checked the valve lash. Everything still in spec. Nothing moved.

What could be causing the noise?

The car definitely sounds different since the over-revs. I'll try to post links to a few short vids with audio.

[DC_neun_vierzehn]

So I thought before I attempt to remove the pushrod tubes to pull and inspect the pushrods for bends, I put each cylinder at TDC to remeasure clearance and rock them back and forth by hand to see if they all felt the same. After ensuring all were in spec (.008 for exhaust and .006 for intake) and rocked them by hand, I noticed that the exhaust rocker on C4 felt like it had more play than other rockers despite all being in spec.

So I took a peek at what I wrote down for the clearance measurements when I first dove into this project several weeks ago:

C1 was in spec (.008 exhaust and .006 intake)
C2 was in spec (.008 exhaust and .006 intake)
C3 was out of spec (.004 exhaust and .004 intake)
C4 was the most out of spec (.002 exhaust and .009 intake)

Also, when initially tried to adjust the clearance several weeks ago on the exhaust rocker for C4, it didn't want to budge. I didn't want to break anything so I took the C4 rocker assembly off. I was able to loosen the nut on the adjuster screw with the rocker assembly off, but it took some force to do so. I reinstalled the assembly and adjusted the clearance on that screw to spec (.008).

I removed the assembly again last week while attempting to inspect the push rods, and noticed the adjuster screw on C4 exhaust valve was all the way out from when I adjusted it to be in spec (.008). See pic below.

So my questions are ...

1. Why would the C4 exhaust valve adjuster screw need to be all the way out to get it in spec (.008)?

2. Look at the face of that adjustment screw end - does it look damaged to you (mushroomed or pitted)? Could it be that when I run a flat feeler gauge in there it's measuring in spec, but because it's pitted (from the over-revs?) the clearance is actually greater than what its measuring because of where it's actually making contact?

3. Is this likely cause of the noisy valves since the over-revs?