Yes, the ones in the catalogs are for 1/2 tons.
I have had good luck by going to the junk yard and picking the master cylinder off a truck with the size brake calipers I am actually using, it's already a factory designed matching system.
Or, go to the parts store and select one form the vehicle you are using the brakes from, if you use the old brakes and just want a new master look for a newer truck with similar sized wheel cylinders, and use that master.
MC mounting details are pretty standard for each auto manufacturer, so chances are that the brackets will work with the proper sized MC.
To design your own system properly read this article, it covers how to properly size the MC.
http://www.4wheeloffroad.com/techarticles/drivetrain/131_0708_4x4_disc_brakes/index.html Grigg
