I see a broken Toyota cam shaft like that two or three times a year. Dangerously high engine rpm's create higher oil pressures. Higher oil pressures cause the cam to "walk" towards the thrust surface resulting in friction & heat which wears away the surface material. This material then washes down into the oil pan it then gets pumped into the oil filter and because the oil filter is under a high amount of pressure, it's internal valve opens and the filter element gets bypassed resulting in the contaminated oil getting pumped up throughout the engine bearings.
Hopefully you've cleaned the timing chain properly and marked all appropriate chain links to make timing the engine trouble-free.
Tony - thanks for the how-stuff-gets-damaged assessment. While waiting on the used cams and bearing-caps, I got everything disassembled and inspected. Caps and bosses - except for the tore-up one - looked pretty good for 142K, at least I thought so. Chain wasn't side-to-side sloppy at all. Followers didn't appear to be marked up - just some discoloration - even the one that had that broken-off flange wedging the valve open (#1-intake, closest to the cam-phaser). I only used the replacement intake cam, and did a "fingernail" scratch test on the bearing journals on both it and the original exhaust cam - used narrow strip of 600-grit emery paper on each - counting see-saw motions 3 times around each one until they were smooth. Used an entire can of brake cleaner on/in each one to clean them, and another couple of cans on the head and chain. In the well next to #1 follower, I used a magnet to retrieve probably 1/4 tsp of iron bits. Got cams in, tensioner snapped in, oil changed (made sure chain got a good dose too), and then cranked it for 15-20 seconds to make sure oil was getting to the head OK. Cam cover back on - coils - and then cranked for a run. Happy to report the initial "stumbles" quickly disappeared and it ran smooth within a few seconds.
I'm just guessing... I found a Pennzoil filter on it - I know the kid would in no way have changed it himself, but I don't know what stop-and-rob quick-lube place uses those products. I noted that the oil that I was blowing out of the wells in the head, with the brake-cleaner, sorta' reminded me of the juice from prime-rib - little globules of fat swimming around - the brake-cleaner didn't really "dissolve" it as much as it just loosened it up and floated it away. The drained oil was also NOT 0 or 5W - anything - it was THICK, and could have very well been NOT synthetic. I'm guessing that was more likely the cause of this problem - too-thick oil, run too long, and maybe made from dead dinosaur skin instead of re-constituted "gas." Will change the oil after a few hundred miles, and replace with 5W-something and a WIX filter. I saved the old filter - will see if Hobo-Freight has a filter-cutter - would like to see what's in it.