The transmission in a 61-64 Catalina is the Roto Hydramatic 375 AKA Slim-Jim.
The Bonneville and Star Chief got the Dual Coupling Hydra Matic, which was far better.
This will help you to understand a little about it. BTW, it looked GREAT on paper!
http://en.wikipedia.org/wiki/GM_Roto...c_transmission