Someone got it all wrong with this bike. There's a lot of work for your 9k......better bikes elsewhere.
Hell you don't have to be a spot the difference competition winner to smell something fishy, they need the lipstick a little thicker on that pig.
Here is 74 for reference, but even if you give them the doubt and say it is 78 it still looks more PE400 than CCM500. As Stan mentioned forks, swinger and possibly frame came out of Hamamatsu, Check out the steering head shape and that the engine does not have as much room around it as a CCM of the same period. B50MX number is good clue that it is B50MX and it also seems to lack typical CCM stuff like trimmed back stepped cooling fins.
Dog of a tank and late model plastics finished off in tasteful black ..... matt black is the Camo of the car and bike world. If someone said it was B50 with CCM side cover slung in PE400T rolling chassis with black painted Don Vesco desert tank, I would think that is closer.