Kawasaki Z400 - cafe racer build

A bit about me.

Well....in a moment when clarity of thought was clearly absent; I challenged a long-standing friend to build a café racer. We're both in our 50s, have been riding forever and would rather be in the garage than with the wife learning new skills and creating something (not quite true; but you get the idea!). Just in case she ever sees this; I'm only joking Darling. REALLY! In any case; if she ever went on this forum; then that would raise serious questions. I've taken apart and re-built saxophones in the past; but am struggling to find any cross-over skills (although I suspect that my ability to find tiny screws on the floor after I've dropped them will come in useful)

So I've now got a decent 1977 Z400 (UK model). It's a great runner and mechanically ok; so the main area of work will be creating 'the look' and trying to eek a little more performance out of it. The reason for choosing the Z400 was because I had one in the 1980s. Not the most sensible of reasons for choosing this as the base bike; but the heart can often be stronger than the head and we have little say in our choices (back to the wife again).

I'm glad that I've taken the time to read various posts and articles and haven't fallen into the trap of just stripping it all down, chopping it up and then thinking what to do. I've got a pretty clear vision of what I want and will post some photos and sketches in due course. This is going to be a long project as I am in no need to rush, want to get it right and am a patient chap.

I have a little bit of technical know-how; but not much and a couple of issues spring to mind. I really want to open up the middle of the bike and remove the panels covering he air-box and replace this with cone filters (I assume that K&N are the best?). This immediately raises some questions. Can this be done (It would appear so from the images of other Z400s that I've seen); but I've read that it shouldn't be done. If it can be done; how do I know which cones to put on and what would I do with the pipe that is the crankcase ventilation system?

We all have to start somewhere and any help would be appreciated.

I wonder now if I'm going to get a load of abuse (the wife theme keeps returning"!).

Cheers for now.

Big Sax