Disc brake conversion kit for an A body Barracuda

No no no... Don't listen to these people with their puny brakes. Bigger is better!

Seriously though, there are lots of options. It just depends on what wheels and spindles you want to run. For sbp, you can't go wrong with Scarebird or the factory KH discs. For BBP I'd probably go with Dr Diff or Wilwood. Again, whichever spindle you plan on using will determine which brake kit you'll end up with.