I put 02 Viper calipers on my 73 Cuda and am planning on putting 18 Mustang GT500 calipers on my 71 Charger. You can use the stock spindle but what you need is a hub, there are 2 ways to get that; you can buy one from Dr Diff or I think Wilwood has them or what I prefer is to use the stock rotor or front drum brake drums.
If you have stock rotors, you can cut off the unneeded part on a lathe or brake lathe. Takes awhile but you get hubs that work well. If you have drums, you can disassemble them and get the hub out of it or you can cut the drum off on a lathe or brake lathe. Once you have the hub you just need to get some rotors with 5x4.5" pattern that slide over the studs (Wilwood, Mustang, etc.)
To mount the calipers of course you need a bracket, there are a few places that were offering brackets for specific brake calipers such Dr Diff, AR Engineering, etc. but I found that you had to use exactly what they were promoting (not necessarily a bad thing) but I made my own brackets.
The way I did it was to mock up the calipers on the rotors (I used Wilwood), then I used some cardboard to mock up a bracket which I transferred over to steel plate. Its not rocket science but does take a lot of fitting, measuring, etc.