The solution for the filler cap is to speak with
www.sandbarcomposites.co.uk (Nigel) they make a really nice carbon unit, I've just received and fitted mine - it looks the dogs doodahs...
I'd thought of machining up some reducer inserts myself - as then you can use the still available 748R type plastic connectors. I'm still hoping for some OE fitment stuff but I'm getting a bit cheesed off with calling Duc specialists around the world to be told that they don't have em'.
Oh yeah don't forget that if you make your own there is a need for the fuel return side to have a non-return valve in the unit !
What have you used / got hold of for the breather pipe and valve ?
cheers
Neil