Help! Small block 360 has a knocking sound

As others have suggested, check your torque converter to flex plate bolts. If only one backed out just a little it will make noises like you are hearing. I was stubborn and didn't check mine right away because I was "sure" I had put loctite on those bolts. Evidently I did not because that is exactly what it was. Won't take you very long to check. Check for exhaust leak too.