I received my fins today, they are made for the k1 rather than the btcc, should be on sale on eBay this week
Still need to see pics of these as I've got a tiny brain and cannot imagine what they look like/how they're fitted without looking gash etc......

Are they literally just fins that are bolted on and not a whole diffuser?
 
sorry completely forgot about this, yes they are from race craft on ebay.

personally i'd prefer a complete diffuser, but one has still not been made yet