Sound tracking gear.
For checking noises from engines my neighbour lent me a" mechanics stethoscope" . It looks like a doctors piece of gear that has two ear pieces and the listening proble is either a steel or wood screw in pointer. You place the pointer on the engine where you think the knock is and listen. As you think it is no.8 rod bearing , if you could listen with a probe on the sump, you may track it down. I had a bad cam and lifters in my 347 stroker, (caused by a "loose" cam gear retaining bolt.) and pinpointed the equivalent lifters/rockers with this piece of gear. Sorry i dont have a picture of it but i think you will get what i am describing here.