I am not familiar with the carb's used on the 56 merc's, but if the choke is of the type with the round black cover that is adjustable by rotating it left or right and retained with three screws, if you are not concerned about originality and you are 12 volt, you can convert it to an electric choke with a little work. I am sure others on here can elaborate more for your specific application. just a thought. I was going to do this to my 51 merc.,but I never changed from the six volt system.----Jim