Ok I’m finding out from other research that 1969 and earlier is typically 50cc and 1970 on is 65cc. The only real way to tell is to pull the head (4 small nuts) and measure the cylinder bore diameter. 50cc = 40mm. 65cc = 44mm. They may be slightly larger if the bore has been overbored from earlier maintenance and installation of slightly oversized pistons. They came in .2, .4 and .6 mm oversized.
