I have the same problem reaching prime focus with my GSO880 and a DSLR, but I work around it using a barlow rather than eyepiece projection. I am able to get enough in focus with a webcam and a QHY5 guide cam, but not my DSLR, can't rack it in far enough.
Generally I think people either fit a low profile focuser or cut down the tube, thus moving the mirror closer to the focuser, to get around it.
I haven't done the maths but I suspect I could get most of the moon in frame if I didn't have the barlow in place. As it is I use a mosaic app to stitch frames together, the results come out OK.
http://www.flickr.com/photos/malclocke/9506224363/
Malc