The engine is an E93A is it a 10hp or a 8hp if its a10 you need to source an 8 hp head for more umph
Aquaplane used to a lot of go faster bits back in the 60`s must still be some around, water pumps were one of the things they used to do as they were never fitted with one, i used to get steamed out regularly in my Ashley back in the 60`s.
Dave