Ok. I think I have a good theory on the demise of this topend.
1. From your pictures, the right side cam caps were BOTH installed backwards. In motor assembly, indicator arrows always point to the front of the engine.
2. Because the head, cam, and cam caps are all "machined together", flipping them around could likely change the fitment. I'm guessing this was done at a valve shim swap by the PO. You didn't list the valve shim specs as you found them, did you?
3. If the cam caps were installed backwards (with a poor fit), torqued to spec, and later discovered "worn" as you see them, then the tight/poor fit could be partly to blame for the poor lubrication which compounded the issue. Once they scored, the torque spec probably went into the crapper and they were later discovered "finger tight".
4. This above combined with low oil pressure caused by a) a leaky oil banjo bolt, b) a poorly fitting K&N oil filter (which wasn't likely filtering the shavings adequately), c) a severely clogged oil screen, and d) possibly the PO under-filled with oil.
And a tip-
Don't bother trying to re-install that water pump shaft seal. Buy a fresh pair.
Also, I've noticed these K&N oil filters don't fit worth a damn. Go with the Hi-Flo variety instead.
"This place fucking runs on beer, you buy the right person a beer, and you get a job, a blow, a place to sleep, whatever.
You're hot, cold, thirsty, hungry... beer will fix that.
Beer is a god damn miracle, and don't you forget it!"