I was looking to do this to my old 9n. I thought that it was mechanically sound and running well so whats the point of changing to an actual 9n3. However, I messaged Chris - scragg9n off clubpolo and he replied with this:
The conversion cost me a grand in total. You need a new slam panel which is basically the front end of your cars structure. Head lights obviously need changing and I don't think it'll be necessary to change your rad but you may need to modify it to attach to your new slam panel. You also need to cut your inner wings so the lights will fit, you'll see were when you come to fit them.
I got scared away when he said it'd cost a £1000 to do it! Though, I did post a link for the full front end of a 9n3, found when browsing ebay.
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http://www.ebay.co.uk/itm/181064987985 Could see if he still has it? Then you'd just have to get it all sprayed and fit.