Uh Oh !! Bad knocking !!

Sometimes you luck out and sometimes you don't. I bought a 1973 340 duster with a 727 transmission that sounded like the rod was about ready to exit the block. A local transmission shop didn't want to bother with it and sold it to me for 250 dollars. I pulled the valve covers and the pushrod was broke through the rocket arm and stuck. I grabbed a used rocker and pushrod off my workbench and an hour later I was out beating on a great running car. Sometimes life can treat you real good
Had the exact same thing on a Jeep 151.... but the valve stuck down and the pistons was hitting it.

As Moper said, time for a tear down if an inspection behind the torque converter cover or under the valve covers does not show anything. Driving will not make it better, only worse and more costly.