Go with what works together, not what might work together. Save yourself a lot of time trying to figure out what's already been figured out. That said I'm using the 73 up spindles, 11 3/4" rotors and the pin type calipers and brackets on my 67.
Totally agree. I love the 11.75" rotors, they're a great upgrade with factory parts and you can still run 15" rims. I have 11.75" rotors with pin type calipers on my Challenger, that set up has worked great for me for over 60k miles of street driving. Stops very well with the 275/40/17's I have all the way around on that car. I was running 11.75's and slider calipers on my Duster before I upgraded to Dr. Diff's 13" cobra style kit. The 13" brakes are a noticeable improvement, but they require 17" rims too. And really, it's hard to beat the 11.75's for the price. If you already have the '73 spindles the 11.75 caliper brackets are $90 from Cass, and you can get the single piston slider calipers from him for $115 for the pair. That's a lot of braking for a little over $200 (assuming you have to buy rotors and wheel bearings regardless).