Since you have an 84, it limits which shocks & struts you can use. I'd suggest upgrading your spindles to 87+ spindles.
The only shocks we have for your car are the KYB GR-2's. Here is the links
http://www.stangsuspension.com/store...idproduct=1347and
http://www.stangsuspension.com/store...idproduct=1348
I'd suggest a good set of lower control arms. These will help with street handling, as well as launches and grip at the drag strip. The Maximum Motorsports Standard Lower Control Arms are a popular choice.
http://www.stangsuspension.com/store...?idproduct=207
For springs, I'd definitely stick with a progressive rate, and a soft spring rating. You definitely do not want anything which is too stiff, and can affect weight transfer. The Ford B springs are a popular choice for 79-93 Mustangs.
http://www.stangsuspension.com/store...?idproduct=260
Sincerely,