Adrian I'd say you'll need an extension tube in place of the diagonal.
I did a quick search and found this link.
Is this the scope you're talking about?
http://www.williamoptics.com/accesso...apter66_03.jpg
Here's the WO page:
http://www.williamoptics.com/accesso..._features.php#
Alternatively Bintel have extension tubes that may suit your setup.