Help ID Benelli Dynamo cc and model

Hi guys,
First post here. Just bought a Benelli Dynamo tonight but unsure on year, model and engine size. I think it is a Dynamo Compact Woods bike, 65cc or 50cc but not sure. Any help or tips would be appreciated.
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.