Not an E body guy so I dunno if there is a difference between manual and power pedals. That adjustable valve is called a proportioning valve. Brake bias can be setup without it, but it takes a thorough knowledge of braking and your specific setup as you will be using caliper bore diameter, pad material, rotor diameter, tire sizing, weight distribution and other issues to dial it in.
Since most people aren't detail oriented and no aftermarket company can cost effectively figure that out for you on an individual basis, unless you are rich, they crutch it with an adjustable valve that is "good enough" for most.
I was naive enough to think I could gather some decent parts, and with my reasonable amount of know-how I could get a braking system that works pretty good. But it is way more complicated than that, I have learned. I am not rich but I ain't broke either but I am not making a show car, race car, or track star - just a cruiser. I believe setting the bias with the proportioning valve will suit my needs. I surely don't want to die or cause anyone else to!
