I never dealt with Passon but I bought a T56 kit from American Powertrain for my 56 Dodge and am very happy with the quality of the kit, responsiveness to my questions and overall experience.
I used a lot of heat and a big hammer to clearance the floor without cutting.... but most cars wont ever be stripped to the bare shell which made that possible for me.
Call American Powertrain they will have the answers about how to get it installed.