Hi Simon,
To take the 2" filters you will need a 2" carousel from
http://www.firstlightoptics.com/atik...for-efw-2.html or
http://www.teleskop-express.de/shop/...--filters.html
I have used Teleskop Express for a lot of things and theyre great and fast shipping, they will answer any questons you have on adapting the wheel to your needs.
From the ATIK website "
if your needing to use a threaded interface on the telescope-side of the filter-wheel will need to either use M54x1 threaded adaptation from another source or the Atik M54/M42 adapter, to reduce the interface to T-Thread"
Also Teleskop Express can help you with the adaptors you'll need. My ORION PARSEC 8300 had a 42mm thread so to adapt the wheel (54mm hole) to the camera I needed a ATIK EFW2 M42 CAMERA ADAPTER (ATIK0098)
I will include the M42 and 2 other adaptors for $15.