Yes it is different on your 03.
Don't know if this helps or not.
I found a YouTube video of a installer on a 2003 996.
fast frog to 2:00 min mark of the video of the dash, they do not remove the horseshoe at all to install the double din..
KENWOOD DNX9960 INSTALL IN 2003 PORSCHE 996 BY AUDIO 200 - YouTube
Hope it helps..