It looks a lot like my 66-18 dated 1950. My machine has the straight lined face plate and back inspection plate. My hand wheel cover is smooth rather than the crinkle on the rest of the machine. Mine has a similar motor and the spot-light. My 66-18 does have the numbered tension dial, but it
might not be original. I have a 1948 manual for the 66-18 and it shows the non-numbered tension.
There were other model 66s that had the spot light as well. A couple of parts lists from
about 1940 would be
http://parts.singerco.com/IPpartCharts/66-8.pdf but it has a different bobbin winder than our machines. It also doesn't include the illustrated plate for the spotlight, but does include it in the list. On page 10 of that pdf it has a chart for the series 4 motors.
The other parts showing the spotlight and some other motors is
http://parts.singerco.com/IPpartChar...4_15_18_24.pdf It appears the 66-14 might be a treadle, the 66-15 is the hand crank version as both have the spoked hand wheel. The 18 & 24 varieties have the solid hand wheel and motors.
The 66-8 parts list shows the fancy face plate as does the 66-18 manual. Can't really tell the fancy plate in the 66-18 parts list. I have found some of these are hard to read, but if you zoom way in one can make things, like the numbers, out a little better.
Looks like a very nice machine. Have fun sewing with it.
Janey - Neat people never make the exciting discoveries I do.