I have slatted on my 55 plate and smooth on my 52 plate and I think they are the same fitting. I also remember a post about incompatibility but I think that was concerned with swapping the chrome bezel, the smooth bezel looks slightly smaller to my eyes, but if you are swapping the whole thing it does not matter. Maybe I am wrong.The method of mounting the service flap and its surround to the bonnet changed with the slatted version. To change from the flat version to the slatted one it's easy, as explained above. But I've read somewhere that it can't be done the other way round - or possibly that it can't be done without irreversible modification - because of the way have you put the bolts in from the other side. I'm sure someone with more knowledge will post up soon.