Hy David C. Baker, welcome, I have a recommendation and a question or two. Do not attempt to use a master cylinder with a bore smaller than the one the truck came equipped with. Your truck most likely came equipped with a Hydrovac brake booster, so I would not recommend a non boosted system. Do you wish to have your new dual system mounted under the floor as the stock single system was, or do you want to mount your new system up on the firewall?