I would get a modern aluminum master cylinder. Mopar Performance sells one, but you can do much cheaper. You can buy an adapter block ~$70 so the 2 bolt holes can be used with the 4-studs on your firewall. I plan to try just drilling 2 holes for an MC from a Breeze (no booster) on my 64 Dart.
To get power brakes (not essential with drums), you need the stand-off brackets w/ lever from any A-body. You can mount just about any booster and MC to the brackets. I used one from a 95 Breeze on my 65 Dart. I just needed to rat-file file the bracket holes slightly. Or you could buy an after-market set for ~$250. You don't need a proportioning valve with drum brakes. I used one to allow for future front disks. The one shown is ~$25 on ebay.