Grigg, AFAIK the residual valves are there purely to stop fluid drain back due to the M/C being lower than the calipers/brake cylinders on under floor applications,so would a firewall M/C even need them??
Whereas the proportioning valve is to provide balance between front and rears.

I've been led to believe the residual valves should be placed as close to their respective ends as possible.
I wonder if there's any definitive answers out there?

It's getting to the point who do we believe? I don't know..... headscratch
Someone out there must know.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.