The "Super High Alloy" that is listed below the one you mentioned is the Z-Spec T5, rated for 330 TQ. For a mildly modified 'stang, that would be the best choice IMHO.
They also offer complete Tranny's and Gear set's along the lines of the G-force stuff, only a little better (and cheaper!) They can handle between 450-500 TQ, are built around a T5 case, so you son't need anything extra like a TKO, and are a couple of hundred $$$ cheaper.