IRS set-up uses a FFR designed upper and lower cage (which is welded to the chasis), and customer control arms. If you are serious about IRS, order from FFR option. You still neeed the center section (rear), axles, brakes, etc.
FFR #4694 (July 2006 Graduate)
Crazy enough to do it with all new parts....
FMS 351W (385 HP), Tremec, IRS, Cobra R brakes, 17" AC III Wheels