I doubt that the fender or the seat are interchangeable. The front fender on the cb350f accomodates the front disk brake and the twin has a front drum brake. The seats don't look the same. That said, you might be able to make them fit.
As for the chrome strip on the seat, it is part of the cover and it takes the shape of the seat pan. Just remove the cover and straighten the pan lip.
The engine and frame serial numbers should not match.