The only thing you would really need is an 8.8 rearend from an 99-04 GT/Mach 1/bullit.
If you want it to be a full GT conversion, you could get GT springs/shocks&struts/swaybars.
This wouldnt be a bad move, but if you were going to do anything, get the Bullit spring/shocks&struts/swaybar...