Can you not park in the grounds though? Fair enough track time as tyou say, would be unfair if it was fully booked up with other makes.
There are normally a few non fords on the stands, although TBH its frowned upon, the carpark though anything is allowed.
If you are going to a single make event, I think its a fair expectation its only that make on display and on track personally, otherwise whats the point in having it single make?
Cliosport saturday though for example, is about cliosport the website, rather than the clio sport range of cars, so at that I think its fair enough people arriving in whatever they want as people use the forum with whatever they want anyway so same rules should apply.
So despite the similar names, I think the two are very different.