Try these links from BAT website and see if this helps in your mods. They have listed UIM and LIM but they are super expensive. You can buy a second hand car instead. Do not buy LIM because your car is already fitted with SVT LIM. Check 'SVT Upgrade' thread for more info. These are BAT links:
http://batinc.net/contour.htm
http://208.109.215.220/files/contour.PDF
This website has listed some parts that are not suitable for our Cougars. Just make sure you are bidding on the right ones. You can post a query here, me or someone will direct you.
With headers, if you want the job easy... remove a/c compressor , engine oil filter and alternator you will be laughing. Dropping subframe wont help you anyway. When I said remove a/c compressor degass and remove it. Dont unbolt and let it hang. The aircon manifold hoses are super sensitive and they crack. It happend to many. Use 3/8" long extension and universal joing with 13mm socket, alternator will come off easy. Access points are one from top through the coil pack to access top bolt of alternator and the bottom one is starting from the diff with long extension. Any other way, you will feel 'why on earth you took up this job'.
Keep checking US ebay for SVT UIM and throttle body or UK ebay. Alternately, you can try newcougar.org (sales section)
Incase you happen to find SVT UIM and throttle body and you have a manual gear box you will need throttle cable from automatic trans. Do not buy SVT throttle cable from US as cars are left hand. So, they are made small and won't fit on our Cougars. Just buy a new or second hand throttle cable from ATX cougar locally.
Where are you located anyway?
cheers