Sump clearance to the rack.
I don't have any pics of hand.
the rack mounts 10-15mm lower for the sump.
It's a common issue people come across when they don't get the right info..
May be Ulsterman if he reads this he may have a pic to show, as he has the 2.3 in his MK1.
If you go onto one of the UK sites (GRP4, Rallydesign etc.)and have a look at the WCXM's you should be able to see the difference with a good eye.