Be safe and convert to a dual master cylinder and a valve if it will be a driver. I have used valves you can have for drum brakes just need to pay shipping. you will need to use 67 line kit
Even with the single Mason jar master cylinders, if you know how to recognize brake fade and how to drive out of it, the dual reservoir cylinder isn't a required upgrade to be safe.
For many years in the 80s my 65 dart was driven daily with a number of miles of canyon driving included in the drive.
There is nothing wrong with the stock braking system on these cars as long as they are maintained.
Yes the dual reservoir is a safety upgrade which can prevent fade, but, it isn't required to drive and be safe if you know your car.
My 65 has 10" drums all around, with nothing upgraded. Yes I have the parts to upgrade to KH Disc have been sitting in the garage for 20 years now, and will eventually put them on it, when I do I will re-line the front and upgrade the MS, but not before.
