What a great picture!
Nice to see cars in their original condition, although that one has seen some severe weather.
Enough to blast the paint off down to the primer.
I got the same surprise when removing my oil pan, sludge. As with yours, my engine was free (not stuck).
Put an oil pump on that has its own screen assembly and removed the screen you show in the picture.
This 1147 engine is a hard one to kill.
Thanks for sharing.