There is a little plate welded on to the end of the silencer with the number on it, mine was at the front top edge of the box. No re-mapping changes needed and I think the MEX1107 was the standard exhaust on the plus 4 from 2004 and the 1105 standard on the 4/4.. put your hand under the car and feel along the top seam edge of the box and you should be able to feel where the plate is, it's about 25mm long but sits proud of the silencer.
