To answer your questions sensibly - yes the face comes off the filler neck, unlock it and lift the tab, you'll need to give it a bit of a tug (yik yik) as the fit is quite tight. The filler neck fits directly to the bodywork inside the boot, there used to be supplied an aluminuim spacer ring but this has been discontinued. You might have to trim your fuel filler pipe down slightly, getting it in place can be a bit of a faff but stick with it! I little washing up liquid will help get the rubber onto the pipes, just a little though. The cork gasket, as mentioned before, goes on the outside of the car. I did this mod a little while back so if you need any more help drop me a line.