If you own a II you have to "think outside the box" to find parts that fit.
Mustang II front
suspension designs are used by the street rodders...hence there were probably brake upgrade kits available before most other models of cars. I bought my front kit in about 1992.
The Mustang uses an 8 inch rear end, again street rod material, hence there are kits.
I doubt you'll find a kit made specifically for the II, but from my experience of putting disks on my car 13 years ago, find a brake kit of the size you want that fits the II
suspension and spindles, next make sure it fits the 8 inch rear end, install a proportioning valve, and remove the residual valve from the stock II distribution block. I was using a master cylinder with a 1 1/4 inch bore, but last weekend dropped it to one with a 1 inch bore to get more line pressure.
There's more to installing it based on the components, but I'd imagine SSBC or Baer should have a kit with those components, just not specified for a II.
Also messing with brakes can be dangerous, so getting it intalled right is very important.
Dave