Proportioning Valve needed

I need a proportioning valve for a 67-up, drum brake...anybody got a used one or can tell me what to buy from Summit or Jegs or ??...
I have a 67 dual res. master cylinder I'm putting on my 66..also what is the difference between Dot 3 and DOT 5 brake fluid?

Thanks...Dave

DOT 5 brake fluid is silicone based, and absolutely will not mix with DOT 3 fluid. If you try, you'll have a milkshake in your master cylinder.