your best bet is to get these items:
Grand Prix 1992-2003 [Flush Mount] - $65.00 : HUmount, Car Radio Mounting Kits

ZZ Performance

ZZ Performance

might need this:
GM Antenna Adapter OEM power antenna male to Motorola cable female at Crutchfield.com

and I have one of these and I love it.
JVC KD HDR50 Radio / HD radio / CD / MP3 player / digital player