I would use your spindles and install the 65-67 mustang factory kelsey hayes disc brakes. You can find complete new kits for around $550. Use the raybestos 36440 master cylinder if you install a used set. I just did this on my 65 Sprint using a set from a 67 mustang.
68-73 disc spindles have the same geometry. 1970 they changed tie rod end taper, and beefed-up the spindle. Otherwise they are functionally the same. Likewise, '74-'77 Maverick and '75-'80 Monarch/Granada are usable (with their own calipers). Lincoln Versailles is similar but requires an adapter sleeve to retrofit. Lots of other choices and sources. Have fun hunting.