Mickey2

You probably will find something with a bit of time and patience. The 66 went throught a few alterations over the decades but essentially stayed the same machine.

The very first had a different fitting for the presser foot, often called a "back clamp", all the others are side clamp and take the regular low shank foot.

There were a slight change to the bobbin case relatively early o .Originally you had to take out a screw to release the bobbin case and clean under there. At some point they made an easier "lift-up and push to the side" type of lever in stead of the screw fitting.

By 1940 when your machines was made these changes had already happened. The next change I know of was the introduction of the stitch lenght lever with reverse (in stead of a turn knob). It happened some time in the 40s, and I think the US factory was the first one to introduce it. The UK machines with this feature are always of a later date than the US versions, all were made well into the 50s. I haven't been able to pin point the date for the stitch length lever, I'm just guessing from what I have read and the machines I come across. This feature were given the subnumber 66-16.

Additional there were a few alteration to the bobbin winder and the thread guides, as well as the top tensioner (with or with out an numbered dial).

To make it a bit more difficult, Singer used different subnumbers for hand crank, motor and treadle, this can turn up as a third subnumber, like 66-10-1. I think the last one indiciates motor, treadle or hand crank. Others who kno will hopefully fill in with more info. Some have favorite decals with this model, some of of the early decals seem to be popular. The simple black and gold machines are nice too.