you can get a 30 series with a 1 inch shaft. i got a brand new one sitting on my shelf in the work shop yet. they are set up for mini bikes with a chain drive sprocket on the driven.
never used it as i got it with the hopes of putting it on a gx390 but my weight and the hp are to much for it i think. you can run higher hp on torque convertors but you need to move less weight to stress it less to make it live. on a mini bike and a 100lb person probily alright on a go kart and 250 lbs not so much