The Aspen spindles will work fine, you may also want to take the proportioning valve as well because you will need to change out the one on your car for a disc brake one as well as the master cylinder needs to be changed.
I see a lot of guys say that all the 73 up upper control arms have the big ball joint, this is not the case. They still used the small upper ball joint on the 73 9" brake cars, I've run into this a few time at the junk yards looking for upper control arms. From what I was told is the upper ball joint size was a mid year change but I don't know that for sure. Just make sure what you have before you start.
Also to those that are looking at using the larger rotors from the Cordoba's and cop cars, these will work fine and you can even use the caliper bracket to convert other spindles to the larger rotor, but you can NOT run 14" wheels with the larger rotors.