I agree with all the previous posts,a 2 bottom would probably be your best bet or like mentioned try a 3 and take off one if you need too. I pull a 3 bottom in pretty heavy soil with no problem with 55HP , it is not only the HP it is also getting enough traction, I will have to go to 4wd if soil is a bit wet etc..
If your tires are loaded , sandy type soil ,you just might be able to use a 3 bottom but I wouldn't bet on it.I would look for a good 2 bottom if it were me .