It is kind of sad that not a single individual has taken this question seriously, so I may as well be the first. My vote would be for a 1951 Ford 8n with Ferguson 2 x 12" plow. That tractor, in my opinion, was the high-water mark for the Ford Tractor company and represents the most refined form of the Ford N-series that the Irish engineer, Harry Ferguson developed in partnership with the legendary American inventor Henry Ford. It is true that the Ford/Ferguson relatitionship was rough by 1951, after the death of Henry Ford, but the 8n, with its red and white paint, was so much prettier than the earlier, all-gray 9n making it far more fitting for a woman of the beauty of Miss Middleton. The 8n and plow would also be a great tool for organic farming on that big estate. That is also the first tractor I ever purchased, sill own, and it remains my all-time favorite make/model.