@ExplorerGuy2007 - Maybe some tough love is in order...
I find you rationalization process and procrastinating fascinating. An engine (any engine) with 340,000 miles on it is not a good candidate for rebuilding. Engines just eventually wear out. If you want to keep your 22+ year old Explorer on the road your best bet, from a monetary prospective, would be to find a running, relatively low mileage used engine and swap yours out. I don't think this would be a good way to go with the Ford 4.0L SOHC V6, as a used engine (even one that does not currently have timing chain issues) is a crap shoot, but maybe you'll get lucky. You may end up spending $800-$1400 on a "low mileage" used engine, doing a ton of work to swap it in and still end up with timing chain problems immediately, or w/in a short period of time. There's no way to know and unless you can verify the engine's actual mileage, listen to the engine cold start and run, don't believe anything the salvage yard tells you.
A reman engine will cost you $2000, or more, to purchase and you'll have to do the labor, buy new replacement parts to meet the conditions of your warranty and returning your core, which they may disallow, or discount based on your core's condition.
Things you mentioned (like having the engine pulled and only having one cassette replaced makes no sense, as puling & reinstalling the engine is the bulk on the labor cost. Replacing your transmission, which you say still works fine, with a another used transmission "just because" makes no sense at all.
You have received a lot of good advice/suggestions from various forum members, but you still say, "I don't know what to do". Personally I wouldn't waste 10 mins on a 22+ year old SOHC Explorer with 340,000 miles on it that has major engine problems (no matter how "pristine" it is) but that's up to you.
Please make a decision and stop asking for more advice as to what you should do. As said, you just keep asking the same questions over and over. Swap the engine, fix it, part it out, or scrap it.
