I recently upgraded from OSC 2600MC to a Mono rig using the 2600MM and ZWO 7 x 2
No issues at all bolting the EFW directly to the tilt plate . I did use the supplied darkening gaskets either side of the EFW
No issues at all with light leakage. I even captured my Dark library indoors during the day without the need to go in a dark room or use a black towel or cloth
I use 8ā and 10ā Imaging Newts so I used the supplied 2mm spacer and 16.5mm extension adapter to achieve 55mm back focus with my coma corrector 

