Randy J,
Things can get mixed up after 40+ years, but a 10 Hp in a 70 or 100 will be large enough to not show much gas tank from the side with hood down, and the gas tank would be "square". A 7 hp would show about 1/3rd of the gas tank and the tank would be oval. A small muffler is just a small muffler. There are other differences, one is the way the steering wheel is connected.
2cents