A few thoughts:

Assuming your problems weren't just caused by a faulty oil pump or the high pressures blowing out seals, etc...

Break-in procedure for a new cam is to run the engine when first started up at 2,000-2,500 rpm for about 20 minutes to make sure the cam lobes and lifter surfaces get fully lubricated. It seems painful to do this to a new engine, but it's the best treatment. If you didn't do that, then that's a possible cause of the flattened cam lobes.

Sounds like your rod bearing clearances may have been too tight when the engine was assembled. I say that because of the wear to copper on the three rods that didn't quite develop a knock. You have to plastigauge them individually as you assemble the engine. It's tedious, but mandatory.

You can re-use the connecting rod. Just clean it up with some emery cloth, etc. and plastigage it when you reassemble to make sure the clearance is correct. No such thing as "shimming" a connecting rod bearing anymore - this isn't the 1930's!

It's possible to polish the crank journal by hand and reuse it too. Check it all around with a micrometer or vernier to make sure it's not oval.

Wear on the tops of the pistons sounds normal; the ring could have been broken when the engine was assembled last time.