Not to burst your bubble, but I really doubt that is a cb500 frame, the cb500 is chain drive, the gl500 is shaft drive, you can see the bike has the shaft drive on the right hand side of the swing arm, there is no way someone would modify a cb500 frame to accept a shaft drive, and the swing arm is clearly the gl500 swing arm. I think you have a customized gl500 motorcycle, maybe with a cb500 front end fitted., unless you fully trust the builder, I would walk away, you have no idea how reliable the bike will be, how well the work was done, and what the insurance companies will cover..