not too sure on size, but I would make a replica rectangle frame of the d/din then another around that, place it ocer the existing stereo slot, mark where it is to go then use a d/grinder or dremel to trim away the edges to the frame fits in place. Once in place glass it in securely from the back using tape or moulding plastecine to stop the resin from falling through the front. Once done remove the tape/plastecine and fill with glass from the front, once its gone off sand the profile smooth. If needed glass some flanges in place for the stereo carcase to hold it in place but still make it removable.

Hope this helps