nanibi,
The 66- indicates it's a Model 66.
The serial number does not match up with the numbers in the ISMACS chart. The numbers that match yours says it's a Mdl 251.
It could be that Singer produced your machine and just numbed it in the series of numbers they were using.
The Singer site says it was made in 1957.
If it has a vertical lever on the pillar to regulate the stitch length it's probably a 66-16. That's a good machine and the price is good too.
Joe