Plus you may need to swap the right side emergency brake cable from your old rear to the 8 3/4. Your original 64 rear has two short cables that hook to a V-shaped cable that hooks to the emergency brake cable that comes down off the emergency brake handle. I'm not sure what year the later setup started, but my 71 8 3/4 rear had one short cable on the left side, and one long cable on the right side. There's a bracket on the left frame rail even on your 64 that will accept both cables, if you just want to convert to the later setup. Then, (in my case) I just ran the original 71 Duster single cable back to the two cables sitting in the frame bracket. Easy, really.
