If the boat is only 33" long, the OS .32 will push it as it was overpowered with the big K&B anyway. It won't be the speed demon that you were used to but it will do the job. you might be able to find a P/S .21 that could have more power than the .32 so that's worth a look at also.
Your next problem is going to have to drop down to 3/16" cable and smaller props to accomodate the smaller engine unless you're already set up for that.
I don't know why you're toting a car battery around as generally we use much smaller and lighter 7.5 amp gel-cell batteries.