I don't think the V shape of the hull is any problem. After all, that is what the tip floats are for. The shape of the step also should not be a problem as long as the line of the bottom of the hull does not reflex back upward and it ends with a sharp cut off. The Sea Cat was primarily a free flight design with a simple radio, usually rudder only put into it. I would go with your best interpretation of the plans. As for ailerons, the plane was designed when ailerons were a hopeful wish among modellers and also, as I said, primarily a free flight design so it was meant to fly in calm conditions so cross winds would be of no concern.
You could update the design by using knowledge which we have accumulated over 50 years of modelling but then, it wouldn't be a Sea Cat.
Just my thoughts,
Peter