There is a seller on e-bay (scarebird) who sells disc brake kits for lots of the early vehicles. A little pricey IMO, but they do look simple to install.
Discs came out in 66,but were the 4 piston type in 66 & 67 and single piston starting in 68.Galaxies,full size Mercs,T-birds(65-66 were different),and Mark IIIs were the same.
what i meant was 65 to 72 is the same car.same front end etc,all you need is the disc brake parts from 68 to 72 and it will bolt onto your car.i would think you would need the axle as well.