Not a very common model, but that helps date it to around 1966. Usually, the first digit in the model # indicted the motor hp. If I am reading the # right, it says 661-7. 7 added on the end means it actually was built with a 7hp briggs. Having a 1 in the model # means it wasn't the standard gear ratio. The early models had a 1 on the lower geared. On the later models, a 1 meant a high geared model. This model was built right when this changed. You would need to count the teeth on the small secondary sprocket ( 11 or 15 teeth. ). I would also like to see what wheel bearings were used. The front forks should have the longer travel springs. Could you measure the space between the front fork tubes? There were forks with 5 1/2" space and the 'super' forks 7" space. Great to see another gote.