You want to use the MAC part number TFA793 (ceramic coated) or part number TFA9358 (non coated). These are long tubes for a fox body stang. You do need to do some modifying to make them work. MaddMartigan has a good post on this, it is stickied in the 5.0 section. The only other choice you have is JBA shorties. SCP sells these I believe.
1993 LX converted to a 5.0/5 speed - Mac long tubes - SCT Pro Racer tuned by Lonnie and me - best E.T. 14.88 - mph 94.59
1991 SC - Stock..........Mostly