It is stamped into the steering head. There should be a white sticker next to the stamped number. The sticker should have the frame number plus the date of manufacture. The engine also has a number, but there is almost zero chance that it is the same as the frame number. Be aware that the modern 17-digit vin did not come into use until the early 1980s.
If you are curious about the numbers, here is some info you might find useful.
www.kzrider.com/filebase?task=download.s...id=1178&catid=64&m=0
