Back to the MC issue. I don't see a problem just changing to a dual MC. It will give a safer braking system. You will have to find or make a bracket to convert from the original four bolt pattern to the two bolt pattern of the new MC. You will also need a longer push rod and have to do so re-plumbing. I like the idea of an adjustable push rod so that it can be made just the right length. The only down side that I see to just doing a MC conversion is that when you change to a new booster & MC you will need to do some more re-plumbing, but that isn't difficult. At that time you will need a new bracket to raise the booster and MC enough to clear the left valve cover. In the thread discussing "Disc Brake Conversion" you can see the bracket and related components I made. It works quite well although I am still doing some tinkering with it.
"Old Betsy" - my '59 convertible J9YJ116209 Thunderbird Registry #33341