Engine replacement for M/T

Thank you for the reply, Joe. I have the full factory service manual pdf download which has the AT and MT removal and install but it doesn't specify to use "xyz" when replacing the engine for an AT or MT car. So, here's the story. I purchased the car from a private seller who said he was a 20+ year shop owner, now retired, who flips a car here and there for extra cash. Test drive went well, I loved the car, specifically sought out the MT. I pointed out a previous front end repair, which he said was a minor fb, new bumper cover and pass side HL. $9,000.00 cash and I was the new owner. Car ran great. For about 5 weeks. Coming home from work one night, I heard what I thought was a bearing whine, noticed the temp start to climb quickly and then smelled coolant. It completely lost mechanical power, electronics still worked, and coasted to a stop on the freeway. Crank, no start. Got it home, hookup up the scan tool, random misfire, cylinder 6 misfire, temperature peaked at 273.2°, hole in bottom of radiator and compression coming out of the radiator when cranked. Had it towed to a shop, who gave me the diag. I did an in-depth dig (hindsight, should have done that before the purchase), found out it was in a total loss front end accident in Maryland at 25,000 miles, auctioned off by the insurance company to a private party, 9 months later a new title was issued in AZ (my state), 3 weeks later another new title was issued (this somehow washed the title of the total loss branding, the title I have shows it's a clean and clear title).

Based on my findings, the engine was used by Nissan in multiple chassis and models/trims. The only ones that varied, slightly, were in the X (AWD) and the Nismo (performance) options, so I believe you are correct in only needing to swap the flex plate for the flywheel. Speaking of the X (AWD), I just noticed the instructions you added in your first reply are for a G37X, those only came with an AT, probably why you didn't see removal instructions for a MT.

How difficult would it be to determine if the engine did get hot enough to replace instead of repair? Would you have to disassemble it to know? For context; my uncle works at a specialty paint and supply store, majority of his customers are local shop owners / workers, one of which he always takes his vehicle to if needing repairs. This is where I took my car per his suggestion. The shop is owned and ran by 2 very nice older gentlemen (both 60 - 70), with 1 other employee. When I dropped the car off and explained everything, the owner said he would look at the car in the next few days to assess the damages and see if he / they even wanted to take on such a large job, depending on what was needed. I say this with a grain of salt, but after talking to the owner again today, I honestly don't think he even looked at the car and based his diag on my info alone. The car is still in the same spot the tow truck dropped it in weeks ago, I asked if he tried to start it at all (it's keyless / push button but it's a bit tricky when the fob is dead, plus I had disconnected the battery after it stopped running since it was brand new), he said he never tried. Which, to me, means he didn't even try to pull codes or freeze frame data. He also mentioned that steel sleeves start to shift when aluminum gets that hot, which requires boring and new sleeves. I assumed he scoped a few of the cylinders or something but having looked it up, that engine doesn't have factory sleeved cylinders, it's a standard aluminum open deck block.

What would be needed to determine if the engine is a lost cause?

Thank you. I'm glad to hear that. I do have a background in the field, though, unused for a while. I attended AAI (Arizona Automotive Institute) right out of high school and graduate in the top 5% of my class followed by 3+ years at a Chevrolet Dealership, starting as a lube tech and moved on to drivability, before leaving the field altogether. I used to be obsessed with Hondas, having owned at least a dozen of them. I've definitely pulled, turn down and rebuilt my fair share of engines, but never anything bigger than a 4 cylinder. As that may all sound like I probably don't need to be here asking you questions, all of that was 15+ years ago. I haven't done much more than a brake job or replacing engine mounts for friends and family in a decade. I'm sure, once this ball gets rolling, I'll have a few questions. Thanks