Do you have the steering wheel? Post more photos of the kart so’s our kart nerds can see what it needs and what can be adapted and so forth.
For the hand controls, I suspect (nearly) any motorcycle clutch and brake controls will work. What is the diameter of the steering wheel rim? If originality is not a goal, consider switching to a foot brake and accelerator. For youths, it translates well to driving and there’s way more positive control in the feet than in the hands. You can really stomp a brake pedal whereas hands get quickly fatigued.
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