Through all the brake experience I have gathered through the years, I can guarantee the return springs have nothing to do with the function of an rpv.  The springs return the shoes back to static position, rpv or not.
In 74, Ford quit using an rpv in the maverick
Disc brake cars. Not sure about others.
The springs will overcome any residual pressure valve in the system and, when you hit the brakes, they are being applied from the static position.  They need to be properly adjusted so that static position does not require a long pedal stroke. I used to get customer inquiries as to why their new disc/drum installation required such a long pedal stroke. 99% of the time it was because the rear brakes were not adjusted tight enough. When people heard a dragging shoe, they though adjustment was done.  Since drum brakes float off center, the drag was just one shoe rubbing way before the brakes were floated to center.

I totally agree the Wilwood engineers should know more than i do about brakes.
Think of it this way.
If the rpv was able to hold the shoes off of their stops while driving the car, that means there is enough slop in the system to adjust the shoes outward a little bit and take up that slack, and the wheel could still rotate without drag.  So, just adjust that slop out and you remove the extra pedal travel.
The main thing is to be sure drum diameter is in spec, shoes are not worn and self-adjusters are in good working condition.
I diagnosed a problem on a 32 Ford once where, after the car sat tor a while, the brakes went away. The master cylinder was under the floor, and the caliper pistons were higher than the master cylinder. They gravity bled back to the master cylinder when parked. Installation of two 2# valves cured the problem.
I have experimented with this. I have two valves on my 66 that made zero difference in brake function. They will get removed if I ever need to replace my master cylinder again. Ford quit using them on disc/drum cars in the 70’s.

Yes, I agree with rpv's for MC's mounted below the floor due to gavity issues. 
And maybe earlier MC's had them built into the MC, as TKO stated. 
I'm just glad to have installed 4-wheel disc's and not deal with drum brakes. 
 

What about original disc/drum brakes on early Mustangs?   The same port on the master cylinder fed both the discs and the drums.  So, no rpv was installed.  They worked.

Raymond_B wrote:

Not that it matters too much but F-150's ran a residual pressure valve well in to the 90's (until they dumped the drums I believe). Not sure how much later, anyway I agree with Steve in that the adjustment sounds off. I remember when doing mine I always lubed the adjusters and then made sure the correct adjuster is on the correct side. I would also run the adjuster out far enough where the drum would slide over the shoes, but had pretty good resistance because I hate spinning that adjuster through the slot. Also, and not 100% sure that this made a lot of difference, but I would apply the parking brake several times as well as backing up and then stopping. That always seemed to get them pretty even.

Sorry if I am repeating a lot of what has been said, but I think it is important to reinforce.

F-150 RPV for trivia  https://www.f150forum.com/attachments/f10/260964d1381187273t-master-cylinder-question-image-3289741942.jpg

Some might not be aware that self/adjusters only function while braking in reverse.

TKOPerformance wrote:

Raymond_B wrote:

Not that it matters too much but F-150's ran a residual pressure valve well in to the 90's (until they dumped the drums I believe). Not sure how much later, anyway I agree with Steve in that the adjustment sounds off. I remember when doing mine I always lubed the adjusters and then made sure the correct adjuster is on the correct side. I would also run the adjuster out far enough where the drum would slide over the shoes, but had pretty good resistance because I hate spinning that adjuster through the slot. Also, and not 100% sure that this made a lot of difference, but I would apply the parking brake several times as well as backing up and then stopping. That always seemed to get them pretty even.

Sorry if I am repeating a lot of what has been said, but I think it is important to reinforce.

F-150 RPV for trivia  https://www.f150forum.com/attachments/f10/260964d1381187273t-master-cylinder-question-image-3289741942.jpg

Is that what that valve is on the LH side of the frame on my buddy's Lightning?  We put a set of brake lines on it some decades back and I remember wonder WTF that was. 

You adjust drum brakes as I do.  I've found that works well enough to achieve proper pedal height and a couple of stops in reverse take care of any remaining adjustment in short order.  By adjusting them that way initially you basically force the shoes to be centered. 

The item that's frame mounted on the driver's side is the rear ABS module (RABS). The RPV is actually screwed right in to the MC and the rear brake line goes in to that.
 

John Ha wrote:

MS wrote:

What about original disc/drum brakes on early Mustangs? The same port on the master cylinder fed both the discs and the drums.

Not true.  There was a unique master cylinder for the disc/drum cars that had 2 outlets on the forward side of the master cylinder.  One port (the lower one, IIRC) went to the disc brakes, the other (comes straight out from the front of the master cylinder) went to the rear drums

Not my experience.  I bought mine with the handling package.  It came with disk/drum brakes.  It's master cylinder had only one outlet.  Not two.  I know because I had to replace it.  Only one outlet.
 

John Ha wrote:

MS wrote:

What about original disc/drum brakes on early Mustangs? The same port on the master cylinder fed both the discs and the drums.

Not true.  There was a unique master cylinder for the disc/drum cars that had 2 outlets on the forward side of the master cylinder.  One port (the lower one, IIRC) went to the disc brakes, the other (comes straight out from the front of the master cylinder) went to the rear drums

Not my experience.  I bought mine with the handling package.  It came with disk/drum brakes.  It's master cylinder had only one outlet.  Not two.  I know because I had to replace it.  Only one outlet.
 

John Ha wrote:

lowercasesteve wrote:

Not my experience.  I bought mine with the handling package.  It came with disk/drum brakes.  It's master cylinder had only one outlet.  Not two.  I know because I had to replace it.  Only one outlet.
 

Ah, then you have an early 1965 model.  Those came with the single outlet master cylinder, which was phased out in favor of the two-outlet master cylinder in the 1966 model year disc brake cars.

That's strange.  I bought it new in June or July of 1966 in upstate NY.  If what you say is true, Ford must have scrounged in their parts bin to find it.  Unfortunately, I don't have a photo.  It was my daily driver in those days and was not anything more than a daily driver.