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.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.