I have an 88 xr 7 .. heres the link http://cgi.ebay.com/ebaymotors/91-1991-ford-mustang-exhaust-headers-oem-5-0-liter_W0QQcmdZViewItemQQcategoryZ33631QQitemZ8069770202QQrdZ1
Yep should fit fine. I have a set on my car.
Of course, they won't fit any of the exhaust parts you currently have on the car. You'll have to change those. Mustang-style H-pipe, flow tubes (extensions), lers, tailpipes, O2 sensor wiring, etc. Several threads on the board describing what to change, and what parts others are using.
the whole conversion instructions can be found here:
http://www.coolcats.net/tech/advanced/50dualexhaust.html