I am lost on what you are saying. My factory '68 Plymouth service manual clearly shows a separate valve (pictured on pages 5-55 and 5-56) being used with the Kelsey Hayes disc brakes. The valve pictured in my book has one line in and one line out. On page 5- 72 (Kelsey Hayes Disc Brake) the "proportioning valve location" is "Left Sill"
The valve in my book is shaped different then the Texas shaped valve.
OK. Not sure where I lost you, but let me try to answer.
Yes. We agree. All disk brake a-bodies up to Jan. 1970 had a seperate proportioning valve from distribution block.
The proportioning valve was on the frame rail, at least by 1967 model year.
IMO confusion is created by calling these parts the wrong name, and when people don't understand the function. Then people can end up putting the wrong parts in the wrong place. Inline should not be describing a proportioning valve as a hold off. That's a different function and used for a different purpose as Chrysler reminded its techs in that page linked in my previous post.
I thought the OP was probably asking about a proportioning valve, and that's the very first illustration I provided. Just in case he was not, or he didn't know he may have been considering a metering valve, I provided the second link.
It definately is hard to find good pictures of the various blocks, valves and where they go. There is an OK picture on page 5-47 of the '67 Plymouth Service Manual. It shows the brass proportioning valve on the rail (sill) being tested.
Oddly, the '68 Plymouth shop manual shows a cast iron prop valve. (page 5-47.) Pages 5-55 and 56 are the Bendix system which continued to use a cast iron prop valve. However, they used the same illustration. Maybe an accident, or maybe simply a part of the decision to combine the K-H and Bendix Master Cylinder service information (starting on page 5-62). Too bad they didn't provide the level of detail given for the Bud Master Cylinder and hydraulics.
To be clear, the early Kelsey Hayes equiped cars did use a cast proportioning valve. It was very similar to the ones used on Mustangs and Corvettes except it was not extrnally adjustable. There's a picture here
http://www.imperialclub.org/Repair/Lit/Master/219/Page06.htm
By '67 it looks like Chrysler switched to the smaller brass valve shown in my very first link.
Also here:
http://www.imperialclub.org/Repair/Lit/Master/233/page06.htm
Some people reading this may wonder after seeing the above picture from 1966, if the proportioning valve must go after the distribution block. It's hard to see but the MC line does go down to a block. Then the line to the rear wheel cylinders is routed to the prop valve.
In 1967 dual resevoir master cylinders were used and with them a 'safety switch' in the distribution block. Inside the distribution block, the safety switch turns on if there is an imbalance in pressure between the front brake and rear brake feeds from the master cylinder. That's why even with dual resevoir, the prop valve goes after the distribution block.
