Hi,
Ok, To answer your question Yes and no. In 68 Ford started with the single piston floating calipers ,These were available on v8's only.These used a specific spindle. In 68 drum brakes used the same spindles whether they were 6 or 8 cylinder .So you have v8 spindles,but you can't run 68 and later style discs on them. If you do however want to run disc you do have options that you can use with your current spindles,you can run the earlier Mustang stuff which used a 4 piston fixed caliper,or you could look into a Scarebird type of conversion kit.