Who makes the engine? Looks good in the pictures. I have done many of these smaller engines and tried many carbs. You need a 2 needle carb so you can adjust both low and high ends. I have used a WT-434 Walbro. They have 24/64 venturi and a 9.53mm bore. Any bigger on the carb and you simply have too much fuel unless you want to scream the motor. I prop and carb the motors I do to run about 7200 or so. Seems to be the best combination here where I am at, sea level and humid. All the carbs have the shaft and plate so I wouldn't worry about it. These carbs are great and in so many applications you wouldn't believe it. Check this link for a hub. Don't know if it is tapered or not but it is a start. Not that simple to just buy a hub as the dimensions are critical. Sounds like you plan to use an electronic ignition. I use CH
Here is what my conversions look like and the parts I make.

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