Are ECU part numbers that critical?.

[unlucky alf]

I have been chasing a problem in regards to the car I saved from being scrapped whereas it  was discovered that no2 injector is doing nothing,

After going through everything it turns out that the ECU seems to be the culprit, Now the thing is finding one of the exact part number is proving a pain mainly due to the two letters on the end of it, I believe those two letters are in regards to the software the car was born with, Also the first block of four digits seem to denote the year, mine starts with 4x43 so the first digit makes it a 2004,

Anyhow as I look more into it even if I get one of the exact part number it would have to be coded in unless I cloned it from my old one, but with the problems my ECU has this may not be possible, Either way it all starts to get a bit too expensive, So my thought was to buy a used complete setup, (instrument cluster+ ECU's etc) from maybe a later year car in which case apart from the injectors having to be coded in, mileage incorrect & wrong VIN number (all of which would be issues anyway) what other problems would I face?.