If no cam bearings spin and there is not evidence of heat or discoloration around any of them, they are likely OK. Cam bearings usually have to be sized when installed as you may have a tight one even when new ones are installed. Consider it rare to drive in a new set and the cam spin freely.
If any main bearings are failed, they may not knock. Evidence of a main failure should be visible at the edges of the bearing at the cap. The bearing will not be fully visible without numerous rotations of crank to give the best view of each side. There should not be any discoloration of any caps and the bearing mating area at the cap and crank should be clean and crisp without any "flaring" of the bearing surface where it meets the crank. If any main bearings are seen to rotate with the crank, it is failed and stuck to the crank and I would expect you to find more metal and maybe even cast iron "powder" which would stick to the magnet.
It is entirely possible that you do NOT find any bearing failure, but it is still prudent that you at least inspect it as best you know how without replacing all the rod and main bearings.
So, inspect cam bearings first, when satisfied none have spun, check crank end play with feeler guage, if ok, then inspect main bearings and caps as mentioned above. Drop main caps that look suspicious. As you said, a rod bearing would likely knock but look at each cap to be sure none are discolored from heat.
If you know anyone with alot of engine experience, a second set of trained eyes would be useful.
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