Carl,
All the hard lines are 1/4". I've had this PU since 1965 and restored it in the early 1970s. The original brake lines were quite rusted so I replaced them all but the size then was 1/4", as it is now.
I thought the way front/back brake pressure bias was set was by using different bore size wheel cylinders.
You are correct, some years they used different bore size cylinders, front to back to achieve front/back bias.
