rebuilding a 1997 300K mile engine with a questionable history.

Hello folks,

I bought a 1997 tacoma from a guy who told me he's a carpenter not a mechanic.

I strongly think he had previously tried to change the head gasket but then gave up when it blew up the second time, and that explains the 2.5 gallons of half oil half coolant in the sump, but the only damage to the head appears to be where he dropped the head on the gasket. There was no damage between a coolant passageway and the oil return holes.
here are some photos. the rust and rust on the valve suggest it was driven for some time on 3 cylinders.
https://photos.app.goo.gl/c9LnHPMFCvir9JeR7
https://photos.app.goo.gl/5Bs36zRDfwYJ9tkh9

I have the whole engine apart except for the timing chain cover because i can't get the nut off the front crankshaft. I changed the rear main seal and I think it had never been changed before, there was a generous groove in the crank but the seal was still very pliable and still sealing pretty good. not leaking much oil through it. i could have just tapped it in a little and it would have probably been good for another 100K or more miles. anyhow.. brown RTV. on both the rear main seal aluminum housing and the oil pan. also brown compound on the flywheel bolts. seems to me anyone in the last 10 years would have had blue loctite on the bolts and black or blue rtv on the gasket.

so anyhow i have new connecting rod bearings and main bearings because as soon as i saw the forbidden milkshake i thought the bearings are toast.. but they weren't. either someone changed them as long as 100K miles ago, or whoever changed the head gasket last contaminated the oil system with foreign debris. i caught black metal debris coming out of the crank today.

so anyhow questions: did toyota use bi metal aluminum bearings in 1997 or tri metal? this truck has bi metal bearings in it that are all foreign object contaminated so i suspect someone changed them.

second question.. cylinder 1 has 3 trouble spots. i think someone had the head off and water rusted the cylinder at 3 different locations at separate times. the biggest wear area has evidence that it was run with said damage for some time.
https://photos.app.goo.gl/Xcd3ZpLmjXASgKfu6
https://photos.app.goo.gl/KmEFWtx5HdQdaERT7
https://photos.app.goo.gl/1W1CmKnMVo7NwYqN8
https://photos.app.goo.gl/QbWzqAzctX7nNWs56

now for the stupid part!
https://photos.app.goo.gl/t9zJWPeaG3Q4RxNZ8

someone took the cylinders out, cleaned them, put new rings in....and did not drill the oil return holes out. 7 of 8 of the holes of the 4 pistons were clogged solid. but under the rings was clean. can anyone explain that?

the crank, wrist pin, clearances are all within normal tolerances, if on the high end slightly, as you would expect for 300K miles..

the biggest difference in diameter between piston and cylinder i can get is .004" across the waist of the pistons to the diameter of the ring ridge at the top of the cylinder.

the cylinders don't have any measurable taper to them. take a combustion ring from one of the pistons and push it down the cylinder and its the same .020" gap all the way down. (should be .011 to .015, which indicates .002" cylinder wear.)
I think someone honed the block at least 100K miles before me. but if they did that, then i can't understand why the rear main seal wasn't changed or the pistons properly cleaned. i honed the block to get the photos currently shown. i think i could have gotten away with not doing so.

anyhow i'm thinking i'm going to put it all back together and drive it for a few years if it runs right. then bore it out for .020" oversize.

I had to machine .005" off the head to get to the bottom of where the head gasket blew in the first group of photos. -and yes i bought arp studs for the head, in case it blows again or i want to work on the head.