So let me shed some light from what I did in the US and am still finalizing for a restored Datsun 510 I am building. I bought a new M274/DE20 engine and an accident damage used M133 CLA45 engine. The M133 is based on the FWD version of the M274 called the M270. All the internals are interchangeable and are forged. They fit with out much need to modify at all. You may need to mill down the deck height a tiny bit. Also I do recommend changing the rings because the m133 has that special coated non sleeved cylinder wall that would cost you upwards of 20k to send it to Germany and a lot of working with AMG to get something similar done with the M274.and you will want to replace the sleeves with either an Molybdenum impregnated sleeves or change your rings and mot the pistons to handle the M274 rings (less desirable.). Next you need to swap the M274 head with the M133 head. You will need a real (not a torch or some other cheap CNC mill to make a custom lower front cover to mate up to the head. You can then use the timing from the M133 and you will also need to make a custom side connection plus putting a couple holes in the passenger front side of the block to handle the oil pump and the water pump for the M133. Oh you also need to drill the block to add an oil port to match the head. Head gaskets these days are interchangeable as they consolidated when they discontinued both engines for the 2020 version in the CLA250/CLA45 and other Class cars that use the new engine. Anyway Unless you have an CNC mill in the garage ( I have a Brother Speedio and a HAAS. because I make parts for a few local race shops as a side business because I was dumb enough to send 50k on the first machine and 75k for the HAAS this is going to be a hard franked motor to build if you want it to be a true M133 hybrid engine. If you do do it though you can bolt on all the externals of the M133 including the electronics, have a local tuner reprogram your ECU to remove all the Mercedes crap that renders it inoperable if you try to use it in any other car BUT you get a legit m133 that can have 400HP with "stock" internals. Obviously I am only doing this as I am building this car to take to a show to hopefully launch a vintage JP Import/Euro shop. The alternative is you can get your car chipped, up the boost. use a ball bearing and a vise to increase your pressure by clamping the factory fuel pressure and a few other minor mods and gain some nominal power. There really isn't much out there if you want to tune these motors not even out of Japan. I will say though that for the car I am putting this in a 2 door Datsun 510 sedan (we got the 2 door sedans here vs the 2 door bluebird coupe.) it makes for a rocket strapped to essentially a car with the wheelbase of a UTV only street legal. Obviously I have truncated a lot of the process here but if you wanted to build one of these you could still use the m133 internals. (Plenty of online Mercedes dealer parts catalogs online to cross reference the parts and most with dimensions available on request or you can get specs from a cracked Mercedes software for the parts, specs, and service info.) You could do a turbo mod and find a Piezo Direct injector supported aftermarket ECU of which only Motec offers one and you have to contact them direct to get the part number and work with a local distributor because no one carries them or scrap the DI and run a Haltech. You could get power that way too. I was able to get my M274 for about 2K new (It was an insurance sale as it had bent studs from shipping and was sold cheap via eBay) and an M133 from a rear ended one that I paid 3k for all USD. These prices were before covid. Just make sure that both have the valve covers intact as these are line-bored to match and can't be replaced despite some deceptive sellers on eBay saying otherwise. Depending on which head you use you can sell the M274 for about 1k and the M133 head for 1400 as used. The M133 block alone can go from 1500-2k etc to recoup some of the costs. All this pricing is based on US costs so it may cost more or less. For example my m133 had a cracked valve cover over the timing area so I bought an additional head from the UK for 700 less that USA prices even after shipping. I am not in any position yet to readily offer any more support than that as I am still building my engine. I have had to make 4 lower front covers so far and there have been some other custom parts along the way but I am keeping the cad/cam files of the complete ones so If I am successful maybe in the future I can offer some support beyond what I have listed here. That may sound counter productive to wanting to start my own business but its my belief that the more people with the information the greater the possibilities that cheaper readily available reliable options become available to the masses and my experience working with the m133 where I have seen upwards of 475hp emissions compliant with just tuning and minor bolt ons this engine and even its host engines the m270(FWD) and M274(RWD) deserve to have an entire performance effort behind them.
Hope that helps. I have a post from another forum based on the Mercedes cars that have the m270/m133 from ages ago with far less info but once I actually complete this I will post more info as I can. 3 kids with 2 in private school definitely put a damp in how much time and funds I have to advance this but I am getting close. Now if anyone knows someone that has a CD009/CD00A adaptor that hasn't had the holes cut for the engine side milled through for cheap let me know as that's what mine is getting mated too.
Until next time!
EDIT. Sorry for some typos but to answer a question I saw. yes the internals are 100 percent interchangeable. If you buy a crate engine from Infinity it comes with ONLY Mercedes M274 serial and identification plates with everything being stamped with the Mercedes logo. It is an exact M274 that Nissan/Infinity purchased direct from Mercedes and only changed external parts. For those wondering there are multiple engines including the L20 from the Z and other engines that Nissan bought from Mercedes and later modified once they could manufacture them so there is a long history here between the two companies. The 510 originally used an L16 which had a modified Mercedes block derived from the L20 inline 6 and a ported head that used the original Mercedes valve train. you know the style you would see in early Mercedes with a camshaft that had the diameter of a cave man club lol.
