It depends whether you want to be authentic. 65-67 Mustang will fit. These
are the 4 piston calipers. Technically, 1967 is unique because it has a
different size thread on the brake line.

If you want to go single piston calipers, then any Mustang 68-73 will work.
Granada, Monarch, and Vesailles will also bolt up but you need a different
tie rod end because the taper is a different size.

You'll also need the proportioning valve and a different master cylinder. On
the 67, It's under the rear seat.  If you go with power disk, you'll also
need to swap the brake pedal.

For a restoration or just upgrading?  Disc brakes were available oem
in 65 as my Mustang was originally equipped. So, another Cougar, or
parts from a Cougar parts vendor, or an after market like Baer Brake
or Stainless Steel Brake Corp.

Additionally, the same Versailles or Monarch conversions used on
Mustangs might also serve. I think you might find in a vendor catalog
some mention of this, as well as in the Tech section of some vendor
web sites. I know some of the Mustang sites Tech Sections have
articles covering this.

Another possibility is to research the articles on the magazine web
sites for Mustang Monthly, Mustang and Fords, etc.

As Spike said...  Tho he couldnt think of "granada' as that's what the
base car is called.
IOW the Granada swap

First verify that your spindle and attaching parts are the same PN as the
same year mustangs.. then find the swap info for that year Mustang

http://www.google.com/search?
hl=en&q=mustang+disk+brake+swap&btnG=Google+Search

Copy and paste both lines