That space is for a convertible top motor as seen in post #301980. Nothing to stop you from trying to put a 6x9 in that space but its not the factory location as already show in post #301955.
They only way to do it like the factory did would be to purchase the speaker housing parts and hardware. There should be more pictures of this if you search the archives.
Couple of observation about the speaker housing some are cardbord and I have seen some in metal. Also the size of them don't offer much room for any good size magnet on the speaker. The factory 6x9 used in them were complete crap much like what was used under the dash.
