If I'm reading it right that is for the kit, then you order the crossmember off a separate page to go with those pieces. I poked around the kit page and didn't figure it out yet but that is the way it reads.
From
http://www.speedwaymotors.com/Mustan...DisplayId=2089
Crossmember NOT included - Add proper crossmember to complete kit.
You must specify POWER or MANUAL in the comments secton when checking out.
You must specify the desired spring rate in the comments section when checking out: 700 lbs, 600 lbs, 500 lbs, or 375 lbs.