I've seen these done by adding a longer push rod from pedal bracket, then mounting the dual mstr cyl of your choice. You will need to fab a mount for the new mstr cyl aft of your stock bracket. Best of luck
You have a nice truck,It is similar to the direction I want to go.I am interested in your carb set up.I have a 235 that I want to put dual carbs on.I also have a Howard cam,and Fenton headers for it.I am not looking to make a lot of power,but want that old school look and hot rod sound.