Yes it is a 1/4" line from the proportion valve to the rubber brake line that runs to the axle, then 3/16" out to the connections to the calipers/wheel cylinders.
My front to rear brake line has a hold off valve on the frame rail, this prevents the rear from appling too soon, I don't know what app you have, but look into it and research it out as I did when I redid my brakes, it is my life I would be saving if they work properly, someone removed my rear hold off valve and disc brake metering valve, always wondered why she would lock up and slide