not to confuse you but I also work for PDX, lol.
You cannot get an immobilizer ECU to work in a non immobilizer equipped car by normal means.
here is an example: another member on this board Slack is doing a H6 conversion into his impreza. his H6 is an EZ30R which is in the 05 model USDM cars with immobilizer. He wanted to use OEM components, I had the pdf manuals and had researched about the immobilizer and told him it would not be possible to "get around" it. He did not believe me and then had to buy all the OEM components to get it to work.
Now, I am fairly certain, having all the components he should have been able to get it to work, but the next issue was getting a dealer to give him codes to program into his ecu, and he couldnt do that without a proper VIN. So, it is not impossible, but if you are starting from scratch you need a lot of money and a friend at a dealer to give you codes.
on a swap if you have all the components and the ecu(all of them being from the same car) it should work, as long as you can get keys for it, or get a dealer to reprogram new keys without the right VIN. Once again you need friends to do this.
The other option has already been stated, run an 04 ecu.
Another option that we have speculated but are unsure about is Cobb may have the ability to flash away the immobilizer function, which we were thinking about doing for our H6 projects until we realized it would be a bitch to do forced induction on the NA platform and it would be more appropriate to go stand alone and MAP based.
Again, trying to get Cobb to do this would require that you are friends or they are nice enough to attempt it for you.
So that is the experience i have had with it, no personal hands on wiring, just theoretical wiring and research. All methods require friends in high places
Not really but you get what I mean. The most plausible option to have it function is having every component to swap out of the same car and the car itself(insurance buy back). Or using a 04 ecu, which may require changing some other components such as the key cylinder or disabling the integrated body unit(I havent looked into it more just a heads up).
hope that helps clarify some stuff. Jarrad may know of a more specific swap we have done or someone has done so that could trump all my knowledge but there it is FWIW.