Im in the middle of trying to figure this out myself. I am looking at a 7"dual diaphram booster and updated master for my 66. Here is my question/statement... and correct me if Im wrong, a more updated master I believe has the porportioning valve built in it doesnt it? Meaning you could delete the external one by the inner fender?
I was doing some hunting and came across these guys. Not sure the quality of the product but they seem to have quite the selection (whether its in stock is another question)
Thunderbird Brake Parts and Power Steering Parts Products