A 60mm thread would make this a good candidate for a Vixen extension tube for something like the VC200L. This screws into the focuser when you are using an eyepiece for straight through viewing, or attaching a DSLR at prime focus.
If you use a star diagonal, you would unscrew this adapter due to the increased light path in the diagonal.
Have a look here at the American Vixen webpage for accessories,
ITEM #2956
I would recommend just obtaining the correct length of 60mm aluminium tubing and finish it in a durable matt black?
Cheers
Dennis