E0SE-A2E block in my 1965 Mustang coupe.
Turns out to be a 1980 Thunderbird 255 (heavy sigh).
Hooked up to a c4 automatic.

Dropped the oil pan today because there is leakage around it and I wanted to check the bearings out on the big ends of the connecting rods. Mmm nice and tight so I think the knocking I hear is the flex plate bolts coming loose. Drained the oil before pulling the pan and let it sit for a while. Sloshed the little puddle of oil to see if it was sparkling and saw a hunk of metal in there.

There was a cap cap or hole plug or something in the bottom of the pan just hanging out. It is stamped 1/2 inside the cup.
Anyone see this part before?

https://imgur.com/a/5Mdjio7

Thank you for that.
Good thing I just replaced the water pump a few months ago and redid the leaking timing cover gasket. Going to test the oil pressure, as I think either the oil pressure light is out or the wiring is dead. but yes, it looks like that is 100% the part.

Thanks again Stepman.

Yes, it is rather disconcerting. Just hope that this didn’t lead to some significant and irreversible damage to the block. Will know more after an oil pressure test.

Oil pan back on after evapo-rust then painting. Installed an oil pressure gauge in place of the oil pressure sending unit. No spark plugs in and spinning the motor with the starter builds 55psi. Thoughts or opinions?

I found this old old post on another forum:
“When I lost a galley plug in my FE I had no pressure and I heard my valve train clattering at idle (that's what alerted me to my gage reading zero and I shut it off).”

Getting 55psi cold at startup. Let it warm up and it slowly went down to 40psi at warm. Jumpers the starter solenoid and watched it oil the rockers on the passenger side. Going to pull the driver side valve cover and verify rocker oiling.