Looking at the photos, especially at the amount of extra space around the empeg mount and the pocket below, I'll bet there's room in there for two DIN sized stereos with the right installation kit and some careful work. Remove the pocket and the mount and you've got a double-DIN opening that just needs the right kinds of coaxing to fit.

Do you know of a nav system which is only a single DIN with the screen? Or at least where one of the two components of the nav system could be mounted in the glove box?