The bigger resivior goes to the disk brakes. The manual brake master cylinder is backwards from the power brake cylinder. On manual brakes, the rear resivior is for the front brakes and the smaller is for the rear brakes. You can find adapter lines a your local NAPA. They have the bigger metric ends on one side and the standard on the other. If you look at the outlet ports and measure the holes where the fluid comes out, you will see that the line size won't make much difference as the holes are the same size. And once the lines are full, the fluid won't know the difference.
I just went through this on my 37. I ended up with a manual brake 68-72 Mustage cylinder with a 77 Malibu splitter/safety valve and for the rear brakes, a adjustable propotioning valve to limit them. I was having trouble with rear wheel lockup. With the valve in line, I just keep adjusting till the rears quit locking up under a hard stop. If the master cylinder is not any lower than the highest bleader valve, you won't need any other valves. Joe
