Tim - Thanks for the education on lifters. My experiences are over 30 yrs out of date and back then I tended to do as instructed.
Always nice to learn proper ways, even if a "little" late.

This whole thing doesn't make any sense, it would seem to be that everything measures within spec, everything that should be a problem has been replaced and yet the noise still persists. After rereading the entire saga, trying to make sense of just what the heck is going on, I find myself coming back to post #22 and #35

"Got it fired up finally. Ran like crap making an awful noise from the head. Sounded like a generator was running under the seat. Limped it home about 15 miles and let it sit over night. Fired it up the next morning and it ran as smooth and quite as could be. No idea what happened but it hasn't made noises in the last 40 miles I've put on it. Going to order an oil pressure and water temperature gauges just to keep an eye on things but, fingers crossed its good to go."

"Lifters came out easy. I got 8 new Meller lifters from autozone and put them in today. The toyota van fsm said to soak them in diesel fuel before installation but I just primed them in a cup of oil before hand."

My first thought was they installed a reground cam and if it wasn't re-hardened, that might explain the 40 miles of quietude but if that were the case, the lift would be way out of spec (wiped out lobes).
Then I decided that it must be those A/M lifters causing an issue, but the issue was present before installing them so that would indicate that the lifters were never a part of the problem, as the likelihood of 2 different sets causing the exact same issue is longer odds than winning the lottery.

I know the vid sure sounds like valve train noise but is there any chance the noise is coming from elsewhere?? did you verify source(s) with a stethoscope?
Maybe timing chain slapping the case or even the distributor not properly seated? Is there lots of oil at the rockers when you pull the Valve Cover?
Something has to be seriously messed up to cause that much noise.

I once had a bad bottom end knock going on at #4, thought for sure I was in for a new bottom end.
Then the clutch started slipping and as I needed the ride but didn't have time for engine R&R, I tossed in a fresh disc & PP.
I did find springs in the bottom of bell housing on disassembly, and once all back together, my "rod" knock disappeared too.
Shocked the heck out of me, but just goes to show, sometimes, noises can travel and send one down the wrong rabbit hole.