I think everyone has done good job in identifying the bike. Its clearly a PY10 from the late 70's. Based on your serial number it could be February of 1977 production but it really depends on the format and type of stamping of the serial number. I previouslt though the 'new' format didnt begin untill 1979 but I have seen a few bikes form earlier years with the new format. Any chance you can post a pic of the number?