depends what spec he's going for doesn't it Chris?
You would never fit a VR6 housing or sensor though, as it's the totally wrong type for an AUM. if you require a larger housing for an AUM, you use the S3 / LCR / TT housing, and you can retain your sensor in the larger housing.
If you're on the ko3S though it's not needed, although many tuners will want one for a hybrid.