Looking for advice on disc brake purchase

The upper and lower control arms that you already have on your 64 are the same thing that are in the picture.
You don't have to change any of your control arms to swap over to those disc brakes.
Just install the disc brake spindles between the upper and lower control arms.
You would change your lower control arms to the sway bar tabed ones in the picture, if you want to add a sway bar to you car. If your not interested in adding a sway bar, leave the LCA's alone. If the ball joints are still nice and tight, get them also. You will need them, or your ball joint mounting bolt holes on your 64 can be drilled out from 1/2 inch to 9/16 inch. That's the difference between drum brake, and disc brake lower ball joints. The mounting bolt hole diameters to the spindle.
If you want to add a sway bar at a later date, the 65-66 sway bars, show up here in the for sale section, or Moparts, bigblockdart.com, and e Bay, or place a "wanted" ad. Just need to keep looking. Good luck to you.
Jim V.