Brenda, I believe you might have a 66 per the pdf I have. Actually, "G" serial numbers can be very confusing. After they got to 9999999 they went to 0000001. Consequently, I feel that accordingly, yours would fall in the range of G-0058326 to 0108325 which would make it a 66 allocated May 28 1923. I have first hand experience of messed up records. I was looking at a 66 in a thrift store, and looked up the serial number in both the first section and then at the other section where they kind of started over. Both indicated that it should be something other than a 66, but I was looking at a 66. A picture would help identify the machine for sure. The "G" serial numbers date from 1910 to 1924. I found some QB links showing the 66 from that time period.
http://www.quiltingboard.com/vintage...e-t249786.html
http://www.quiltingboard.com/vintage...r-t215285.html
http://www.quiltingboard.com/vintage...t169005-2.html
As Leon asked about the "dog tag" on the front above the tension dial would confirm it being a 27, 28, 127, 128 (all similar and made during the "G" numbers). Also they have slide plates that go from front to back of the machine with a circular needle plate.
The 15 and 115 had tensions on the left side of the head.
I would also suggest reading through the sticky
http://www.quiltingboard.com/vintage...v-t167789.html Basically, it is suggested simply wiping down the machine with sewing machine oil on soft lint free cloth or cotton balls. Oil all the places indicated in manual, if you have one. or where metal meets metal. Singer has manuals available for download at
http://www.singerco.com/support/instruction-manuals
Some of the 66 models of that era had back clamp feet and some didn't or were changed at some point to be able to use regular low shank feet.
Janey, Neat people never make the exciting discoveries I do.