Most things are the same, you can use a 2.0 bottom end with a valver head it you want. If you are just using a 2.0 bottom end you can also use a megane 2.0 engine as long as its an F7R, though you would have to change the flywheel to a valver/williams one. If you just use a williams engine you can pretty much re-use everything the only things you will need to change are the ECU and possibly the starter motor iirc. A good alternative to a new ECU is just to chip your valver one, there is a guy on williamsclio.co.uk who sells chips for about £30.