JDM engine suppliers / Head Gasket Fun / Engine swaps

I've been reading old threads on JDM engines. I was under the impression they are low mileage engines that were used in Japan, and swapped out due to the lower threshold for admissions.

However, some of the posts are calling them salvage. I don't want salvage, and I'm not looking for a rebuilt engine.

Details on car: 2011, 206,000 miles. Brand new Toyota hybrid battery, water pump, and brake booster all in the past 1.5 years. 12 V battery replaced three weeks ago.

Engine light went on last week, after the cold start up shake. Codes read misfire.

I had to bring in the car to have the front rotors and pads done under warranty, mechanic said he didn't do anything else. But when I picked it up, the check engine light was off? I don't trust this guy for other reasons, so I won't be going back to him.

thing is even though the engine light is off, the coolant is slightly low, and it does shake intermittently in the morning. Being a 2011 and having sunk close to 6K into all the other upgrades, I don't want to waste time diagnosing known problems.

Cost wise, it seems to make sense to swap out the engine versus replacing the head gasket. Especially looking at the amount of money I have in it. This way I get more years out of it, and it's cheaper.

Is it worth swapping out the engine and the transmission at this point? I'm trying to determine if Ican make it last another eight years versus walking away and buying an another used car.

All said, I'm in Asheville, North Carolina, What are some reputable, JDM suppliers, and are they low mileage swap outs from Japan, or salvage engines? And then, of course the transmission question. If you got this far, thank you!