I know this is super old, but thanks for the picture and the idea.
I was just about to order an in-line proportioning valve for my 4 piston brake conversion, but this is a heck of a lot slicker looking.
Just ordered myself one and will mount it in place of the stock splitter.
To be honest I've never had to adjust it, It has always been wide open, you might get by with out it?
I'm not convinced I will need it, but in the relative schema of things, $67.99 for a proportioning valve I may need to help the car drive a little better and be a better summer DD is all right by me.
I gotta get all my front end projects done so I can drive the damn car before June - the brake system is the only thing I needed more parts and pieces for.