76 Dart Front Big Bolt Pattern Disc Brakes on my 66 Valiant??

You most definitely will want the lower control arms from the 76 if they have the sway bar tabs. While the '76 sway bar will not fit the '66, you can use a bar designed for the factory mounts for a 64-72 A-body.

All of the aftermarket sway bar mounts I have seen use flimsy tabs that are attached by the lower shock bolt. Furthermore, I've seen problems with aftermarket bars and 73 & > calipers interfering with each other.

You may also want the rear axle so you don't have to have two spares. Put the emergency brake cable from your car into the '76 rear brakes. There's no other conversion needed.