The rear for 5 lug can be accomplished several ways. Redrilling the axles and drums is the basic soution. have a machine shop weld p the 4 lug patttern and go to the 5 lug pattern of choice. Next is the bone yard aproach. Any 64-66 Mustang is the same drum to druma dn perch to perch measured axle as a MII. Meaning that the axles will directly replace for length and fit. find a 5 lug 64-66 Mustang or 63-67 falcon, or newer Versilles amnd get the axles, brake backing plates, drums and shoes and you are done. NOW note if you do the bone yard approach to make good notes of what you have because n the future you will order brake parts for the donor car not the MII. Lastly is the rearen swap.
The Versilles disc brake 9" is the rear os first choice, bolt in convenience, drear disc stopping power and easy Emergency brake adaptaion. understand though that the 9" is heavy, and inefficeint. Also, the 9" really only offers about a 25% increase in overall power handling capacity over a well built 8" so I only recommend going to the 9" in extreme cases and stilll would weight using an 8.8" from a newer