I have taken apart both the MK2 and MK2.5 instrument clusters and can say for sure (internally) they are completely different. The layout may be looking the same but the size of the dial plate and other components are different. The MK2.5 front fascia will not fit onto the MK2 cluster. Because of the different size of the dial plate it will partially block the MK2 dial plate I already tried this in the past.
The MK2.5 dial plates are a bit smaller then the MK2 dial plates. The needles are shorter also. The warning symbols are ont a different position also.