the vin number, based on a write up provided by someone else... I remember the 78-79 range by heart from when I was looking mine up. This may be inaccurate, since its based on second hand info, and there are some gaps in those numbers. You are welcome to keep looking... provide some pics of your bike and these guys will be able to tell you what have based on that as well.
1978s ranged from 000101-100101
1979s ranged from 150101-250101