Looking for advice on disc brake purchase

robjkc.
I think that's a decent price to pay for all those parts, that are included in the picture.
Even though your most likely going to be needing new rotors, (they look worn, and chewed up), and rebuild kits to go through the calipers.
The sway bar most likely won't fit on your 64 Dart GT as its "narrower" than the 67-69 other A body cars. So that sway bar is going to be to big from center to center measurement.
Whatever you can't use, you shouldn't have any trouble in selling off the unused parts, or just keep them.
The lower control arms with the sway bar mount tabs on them, are worth decent money individually, along with the sway bar.
You found a good stash of parts. Good hunting. Good score.