Phew, I thought this thread was going to be about finding a jar of NOS 1970 Dot 3 brake fluid or asking if someone has some NOS 1970 brake fluid specially designed for a Dart.
This a trick question, this morning?
As much as it might take to bleed out the master cylinder, and brake system, as necessary.
Who really knows, at the start.
Buy yourself a quart container, to start out with.