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There's certainly a lot of trash in the bearings, but I think some of you are really overlooking the obvious cause of failure. Take a good close look at the wear pattern on those mains and think about it.

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Okay,

Boy , I see lots of stuff.

1. Lots of trash in the oil.
2. Uneven wear patterns.
3. Wear at the parting lines.
4. Heat build up burns from lack of oil.
5. Apparent crank contact on all bearings.

Those are the symptems that I see, so what do they mean.

My guess.

Combined issues,

trash in the oil
main bearing bores out of round
bearing clearences to tight
lack of oil flow at some point
maybe poor assembly with grit on back of bearings
any or all of the above

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Most everybody just assumes it's a lack of oil. It may or not be. Take a look at the wear pattern on the mains all the way up to the parting line. given that there's at least .003" of ecentricity built into the bearings, that tells me right away there was insufficiant oil clearance. A good portion of the trash may have very well come from the bearings. I'll say this also, when a machinist finishes working on your stuff, they typically clean the worst of the debris from it whether it be a block or a crankshaft or most anything else. They don't clean and prep it for final assembly unless you specifically ask them to do it. That type of cleaning generally comes with an additional charge. It's up to the person assembling the engine to make sure everything is spotless and ready to go.
When you see a bearing into the copper it was either starved for oil or had no oil clearance to start with. Since the rod bearings don't seem to be into the copper, my guess goes back to lack of oil clearance on the mains. It's pretty obvious the heat on that one bearing caused it to lose its temper and it wouldn't surprise me to see a slightly bent crank and signs of bluing as well.
The block needs to be closely inspected and probably align honed or bored again. (I prefer boring over honing)
Just because a block is align-honed and the crank was ground does not mean oil clearance is automatically okay, nothing could be further from the truth, actually.
I have teo engines in the shop right now that look alot like the OP's. One was built by a local machine shop with less than 5000 miles on it and the other by the owner with ZERO miles on it, just cam break in time.
My best advice would be to take nothing for granted when it comes time to put it back together. Enlist the help of a competant machinist to cage the bearings and measure, or at the very least, someone with the right tools and the experience necessary to do the job right. You can't have any engine part too clean, so when you think you got it spotless, clean it again.
Best of luck.