@Kevin2511 I looked at your thread in the Large truck forum. I noticed your truck has a Hydrovac booster. It has been a long time since I have owned a large truck, but I don't believe a dual master cylinder is going to be compatible with the Hydrovac booster. Here is a thread from the large truck forum that may be helpful. Good luck bleeding that thing.
Brake data for1960's Ford N or F600, etc - Ford Truck Enthusiasts Forums

 

Is the below the current install?




Also look for any CASTING ID on the current MC -