Gen 8 Galant auto - spare auto and TCU compatability

[Kay]

Just trying to be pro-active in case I need the info at later date; I have a 2002 auto and due to concern about spare parts, I bought a spare auto that came up for sale. Once I had it I read somewhere that one has to have a TCU for that auto, so a little confused. I did end up buying a TCU that came off a legnum, but was told it would work. So wondering how can I research if my auto would be compatible in my car if needed, as I notice it has an external oil filter which I don't think mine has. And if it was fitted, would it work with existing TCU or would that need to be swapped out. I can check part numbers and serial numbers if someone knows what I should be looking for. I may never need it, but I would rather know - TIA