Clois,
The Wilwood 'Heavy Duty Front Brake Kit' for the Mustang II is 140-2129-B. The slotted/drilled rotors are a special order from Summit. The Wilwood instructions say to add a 'D' to the end of the kit number to specify drilled (no mention of slotted).
Since Wilwood is local to me, I actually bought the non-drilled/non-slotted kit from Summit and then went directly to Wilwood and exchanged them for drilled/slotted rotors. Wilwood charged me full SRP for the upgrade so this actually cost me a bit more than if I would have special ordered them form Summit. At the time, I needed them asap so it was worth it to me.
Here's an exploded diagram of the Mustang II kit. BTW, this is a 'bolt-on' kit with no welding needed and, except for the spindle nut & washer, it includes everything you see in the diagram (even the hub).
Hope this helps.
Gene