Engine swap and part compatibility

The engines themselves will usually carry over if the code is the same, but you usually need to transfer the manifolds and exhaust parts over as well as things like the O2 sensor(s) from the original car because of the emissions differences in the model year. Toyota does sometimes make changes between years like compression, but it's rare for them to do that being Japanese (at least without an indicator like a different part number or engine code). If it works, they do not touch it unless the federal government (or California) forces them to. In those cases they change the engine code to make California happy so we can tell, or make 2 engines with the same standard code but 00 is CARB and 01 is non-CARB (ex: 2AZC-FE and 2AZ-FE).

However (while high mileage isn't a worry for Toyota) make sure if you buy a used engine you know the original mileage and make sure it isn't too high for the year involved; while Toyota engines are cheap a lot of the time, they tend to have more miles on them then others when they get pulled from the cars; 200k+ mile engines will come up more often. If I'm running a car like a Toyota to 200-250k+ miles, I want to put it on there and do the maintenance and not hope someone else maintained it. Same for the tranny, if you leave old ATF in there and switch it too late it will slip and need a rebuild. I also don't always know if it's an oil burner right away like some engines like the 2AZ-FE are known for (unless Toyota rebuilt it under the TSB those were covered under for YEARS). However, if I got it to 250k miles, I know the engine and oil consumption rate because I watched it over time, it's not unknown. Old high-mileage Toyotas (can and often do) burn a little oil, especially with known issues or bad engines with known issues; unless you change the piston rings and do a rebuild on it to mitigate the issue, they will always consume some oil. The reason I would want to know especially on a Toyota is people will run old high-mileage Toyotas as beater cars even with 500k miles; which is fine because they will probably be fine at that mileage and get to 700-800k on the i4/V6 engines but would you want to install a 200k+ mile engine with no known history? They maintain the car with these high mileages because it's not worth enough to sell once you get to the 200k mile club on a Toyota and anything higher is worth more dead. 200k miles on a American car never ends as well as it does on a Toyota or Honda, ever.

Japanese companies who do it right change the engine code to make the government happy, not the specs. Toyota IS one of those companies that doesn't use the same code for years but changed the emissions design or compression (ex: 1995=1:2, 1996=1:4 CARB, 1:2 for everyone else). This kind of CARB-certified nonsense is obvious (even for Toyota) as the CARB engines will have a different part number because California is that level of nitpicky about CARB certification. The build sheet will usually tell you unless the CARB engine is used in all 50 states. However those of us in normal states will generally use a bad engine as an excuse to rip out these nonsense CARB engines when possible as it tends to be cheaper to do that vs finding another CARB engine.

The ECU/immobilizer pairing does not impact things like engine swaps, but you may need to keep the electronics matched between the cars in that case to avoid problems. In a non-CARB state getting rid of these CARB engines when it isn't the standard type tends to be cheaper as there will be more non-CARB engines vs CARB engines.