Proportioning valve question

If it is working, and could be cleaned up nice, I would go ahead. It also depends on the use of the car.
Just an opinion

 

The valve provides different pressure from the single chamber master cylinder to the front and rear brakes. Your front discs take about 80 percent of the brake pressure. There are after market adjustable units with large knobs that are easier to use when you are changing driving styles based on street or various track configurations. It is a valuable piece to keep and a real PIA to repair. I pulled mine out to replace with a after market one for easier adjustments (available from most brake supply vendors). However, the original sits in storage for when it is needed for car shows.

 

Good info on the valve and rebuild advice at www.stangerssite.com Look in the "other stuff" at the bottom of the home page.