Rob, you're right, they look very similar, and that was intentional. Harry Ferguson invented the 3 point hitch, and had a famous handshake agreement with Henry Ford that he would get a fee for each Ford tractor sold with one. When Henry died, his son took over, and said that since the agreement was never in writing, he would no longer honor it. Understandably, Harry was very angry, so he designed a tractor to compete with the Ford "N" series, which was their best seller. The TO-20 had some improvements over the "N"s. The gears of the "N" series make it difficult to use for mowing, because of a high ground speed. The TO-20 has a greater speed difference between the gears, making mowing and other functions easier.
As far as appearance, one of the easiest ways to tell them apart is by the hood. The "N"s have a lid over the battery with a little ornament, and the Fergusons have a solid hood. The grills are also very different, but I don't have pictures to illustrate this. What amazes me, is my tractor is 50 years old, and runs like a top! How will todays tractor's run in 50 years?
Rich