The Letter "U" in the model number stands for Universal. In other words that carb. will replace several models of carbs with the same mounting flange. When you look it over you will see how the throttle shaft and choke control will mount in several different ways, even from one side io the other.
Take it from someone who has used one that was for a super 44, super 55, 66, super 66, 440 and the early 550's. I could never get the tractors to run right with that carb.
If you want your tractor run right, get the correct carb. (TSX 120) for your tractor.