Viper brakes 73 dart

Ok, so I know there are several posts on viper callipers, I am still a little confused.
I have been trying to look at ar engineering, but their website appears to be suspended, are they still in business?

I have a 73 dart, w disc brakes already.
I have ready that you need drumb front spindles, is this true? cannot I not use my disc spindles? If I need drum spindles, i have a set from my wrecked 72 dart, woudl those bolt onto the 73?

Aside from are engineering, is there anything else i need to buy? besides calipers and rotors?

Thanks in advance