I'll attach a piccy of the back end of mine to show what an evenings work with a cordless drill can do -
I didnt realise the 'trumpets' were missing on my airbox until I read this thread - but nevermind, more weight saved.
Mine came with a K+N fitted already but I would of bought one straight away simply as they can be cleaned and re-oil, try Nelly first but I got my cleaner and oil kit from :
PDQ Developments If u can afford it - I think in hind sight (a wonderful thing) I recommend going to a good tuning centre that has a dyno with a gas analyser, get them to fit your K+N and dynojet kit and then if there are any 'tweaks' that need doing (eg if the jets are a little out for your bike) they should sort it all out for you.......
Sadly, I think you will be looking at £250 ish for all this to be done but hopefully, it would be worth it.....
Cheers - Frank