Disco 2 replacement 44hp22 auto box

Hi, I want to replace the auto box in a TD5 disco 2 2004 plate,( fitted with a 44hp22 box), with a used unit, I've been told that the model numbers of both my unit and a replacement used unit have to match, (ie the 1043/010/770 numbers) does anyone out there know the relevance of matching these numbers or will a unit from a similar vehicle work just as well?
Has anyone been successful in replacing their auto box with a used unit??
Cheers.