Scored Main Cap Bearing - Ouch

I have done this on a different engine......put in diesel and pumped it through the engine with a priming rod, while turning the engine over slowly by hand. Drained the diesel a couple of times. This was to clean out the mains and rods. Then pulled lifters one at a time, starting closest to the pump, while priming, to clean out the lifter bores with diesel. In this engine, you'd then have to clean out the rockers shafts and heads. I then pumped cheap oil through with a coupla changes while turning over slowly times to clear the diesel out. Then put in the oil I wanted and changed it after 5 minutes running, and once again after 10 minutes.

It was an engine I did not care a ton about, and was done to get coolant out; did well for that, but IDK on metal particles.

How about a pix of the #8 rod bearing and journal please?

Inspect the oil pump if it was new at rebuild. If it was new and you see a lot of scoring and chewed tips of teeth, etc., then you know metal particles were pulled out of the pan. The pump is before the filter. (If it was not replaced at the rebuild, then inspecting it won't tell you anything.)