the only mod I have got on the zenoah is a boost induction systems boost bottle.
some people thought it was a nitrous oxide kit but in fact it only recirculates surplus fuel inside the carb into the bottle to be put back into the combustion chamber when needed automatically. the result is a much smoother running engine with slightly more power,but not too much as to overstress the engine components.
the silver object on the left of the picture is the boost bottle. The carb isolator block has to be drilled and taped to accept a large angled tap for the boost bottle line.

here is a close up of the boost bottle angled tap and the stainless steel heat/scuff protection sleeve covering the bottle line and watercooling line.

I passed the end of the pipe completely through the transom so I could attach a silencer if needed,this pipe has a large internal water jacket that is not reliant on o-rings to keep the water from leaking out.

the cheapest and best drivers are the one's you can make up yourself,I made these out of a couple of my sons 'spare' action men cut In half just above the waist,and fixed to the hatch with small angle brackets and nyloc nuts and bolts.
the 'head' was the cap of a bubble bath bottle In the shape of a well known 'tame racing driver' from top gear called 'the stig'!!!!