I had one look about like that, a little browner gunk. I kept running a small block 400 with a cracked head. Shattered described it better, or them, both heads cracked all to hell! Mix water and oil to get that nice sludge. I was taking a trip back and forth in the vehicle and I would pour bleach and detergent down the radiator to flush things, fill it with water and go!
Funniest story was one an employee told me. He bought a rebuilt 327, installed it, hauled it back a few days later. "This motor is no damned good!" They gave him another one. Eight or ten years later the mechanic and the man that sold him the rebuilt engine were in a bar drinking and the man asked for the truth.
"You know my oldest daughter has epilepsy? I had just swung the engine in the car and filled it with oil when she had a seizure. I took off to the hospital with no water in the engine, a twenty minute trip or so when I poured the coal to it. I turned the engine off and got my daughter checked in. When I stepped out the engine had kicked backwards and was still turning backwards. Whatever, I kicked the starter in and the car cranked. Drove it back home, still no water. The next day I tried to start it out of curiosity. Locked up tight!"
The 327's were tough but there were limits! Still one of my favorites to make a screamer out of.
Hu