Do you have an idea of how many rpm you want to turn?
You'll need to know the OD of the rear tires too. Are you staying with what looks like slicks in the rear?
I don't know if you've posted what cam the motor has because you'll need to stay in the working range for the cams rpm ..
There are many estimators online. drop in the tire size and the gear selection and it'll tell you the rpm you can expect.