Hemikiller is right, take a look at this site.
Dennis is great to work with and has very reasonable prices.
Also, if you have a small bearing 8" or 9" rearend you can use the rear disc brake set-up from an early 90's Crown Victoria. You just have to grind off a small piece of the backing plate so that it mounts flush against the flange, and then everything bolts right up.
My power 4-wheel disc brake set up works extremely well and all of the replacement parts are very inexpensive at any parts store.