Pieces of steel in cylinder??

Ima thinking this is not from the pounding on the rods. That rod bearing has not been pounded hard nor has material melted out of it..... it has had some bits of soft material pounded into it, probably coming in the oiling system. No wonder the crank looked decent, and no way all that soft stuff came out of the bearings. So coming down from the cam bearing area or head/rockers? Or coming in from the main gallery?

OP, when you get around to it, pull the plugs out of the rocker shafts, particularly the driver's side. If the cam bearings was involved, then some small bits might conceivably been pushed up there. They need to be cleaned out any way, just like the engine passages.

With .040 on the bearings in there already, this crank has been seriously turned down before. No wonder the mains looked so thick in the pix. If the crank is not perfect for diameters, I'd not expect to be able to find any bearings to use the crank. Rock Auto has .040" undersized bearings as their max size. Sorry 'bout that.....

What do you plan to do with this engine/car? Just trying to see how it may be stressed in your planned use.