I am certainly no expert about shimmed main or rod bearings, but back in 1964 auto mechanics class in high school, Mr. Parker said the first thing to do with an engine with a knock is remove spark plug wires one at a time to try to isolate the noise to a particular cylinder. I think that would still be good advice.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.