as far as im aware lotus never made an extended roof vent, there just what people have had made so you will see a couple of different ones knocking around. The engine cover Lotus did make so people have had it copied so they should all be the same.
Thanks for all the replies guys, I have been out of the country or would have posted sooner.
I have decided to go for the extended roof and the motorsport rear clam.
Neil your car looks really great which is a good sign as Plans are actually making up, fitting and blending the parts for me as part of some expected and unfortunately unexpected work! ( They are making up a wider scoop as I prefer it )
As well as the usual K cooling problems I have some custom motor/hydraulic work in the back of the car that the addition of the wider roof scoop airflow and the swiss cheese rear will hopefully help to keep cool!