Kz650 carbs woes

Hi, and thanks for the add, I'm from the UK and have recently acquired a 1980 kz650 I'm steadily trying to get running.
I need a bit of experience regarding air box and carb issues, some parts sfor the Kz are quite rare here in the UK and I'm missing the airbox, the bike came with a chopper style chrome air box but I'm struggling to get it running correctly, through past experience of working on old bikes I know that generally bikes tend to work best on original air box's... But I can't get hold of one! Would anyone be able to recommend a alternative that might be workable.
Thanks

He offers an original air box in realy good condition for 29 Euro.

www.piets-youngtimer.de/KAWASAKI-Z-650-SR-LUFTFILTERKASTEN