I would use a later dual drum M/C, like from a 68 Fury. It will bolt in place of you existing M/C.
What are "HD brakes"? that is unclear.
Do you mean power brakes?
You will need to mimic the all 68 drum setup for the M/C connections.
Front port connects to the rear drums. Rear port will T to the front brakes.
The car has the 11 inch rear brakes. I am going have to verify if it has power brakes, I don't believe it does. If it is a manual brake car I assume it will require a brake pedal rod to match the master cylinder? The car is at a local shop and they called me to help them find a master cylinder. I've never done one but I knew it has been discussed here a lot and I would get pointed in the right direction.
Thanks!