Circa 1912 - 1916 - Early examples of the 3240 have the chains connecting the two trucks. The bodys  are formed from 8 separate pieces. The early versions have 2 windows cast into both ends of the cab. At least one example of the above locomotive has been observed with green trim and was found with three cherry red cars lettered for the PENNSYLVANIA.

Enlarged photo of early  (bottom) and late (top) - besides the chains and non-aligned axles on the early example note the 'ear lobes on the side of each truck on the end.

The example above is early with the chains, offset axles, and note the 'ears' on the end of each truck.

This one has a chain on the front truck and one from the bell. We've never seen another like this and didn't examine this one personally, so it's just a picture.

Circa 1916-1920 - later model gray 3240. This version has no chain between the trucks. The axels line up with the outside journals and  the cab has no end windows. 

This is a late 3240 - you can tell as there's not cab windows on the end and no chains.

Late model 3240

Every once in a while you're find a 3240 marked for the New York Central lines, these actually came with 180 series cars in greeen also mark the NYC

Bottom of a late 3240 showing the power truck and the pickup on the dummy truck.