How did the knock start? It would take a fairly good hit of water to bend a connecting rod, or a big shot of Nitrous Oxide!
Old engines are very easy to work on, take one step at a time and we can walk you through it.
Pull the valve cover and check around for extra loose rocker arms, even start it up with the cover off and look and listen. If everything looks OK, pull the oil pan off, it needs cleaned out anyway. Check for loose rod bolts or main bolts, or signs of heat or stress.
Give it a try before sending it out. Joe
