Search. Several posts on this in the last few months w/ photos. New after-market ~$250. I went cheaper and used a booster/MC from a newer car on Dart stand-off brackets (search).
I wish that I had some old pictures of the car when I put the power disk rear drum set up on the car. I used the scissor(if that's what you call it)set up off of 74 duster with a small booster and cleared the hood and everything else. I ended up putting the same set up on my BB 1986 RC for ease of maintenance. I do have a picture of that.
I've been using Dr. Diff a lot for brakes and rear end stuff over the years.