It is the fins in the crank case that is the best identification, the newer model have the top three of case with a larger diameter.
The head can be anodized or not, but the different outside of the crank case also means that it has a better matching on the ports on the inside. The solid alignment pin for the cylinder is also a telling improvement, the early ones had a hollow pin that would release crank pressure (visible with a magnifying glass or the bubbling of oil during running.