Yes, there's been some parts swapping going on, lol. These bikes were so plentiful years ago, you often stumbled upon parts cheap or even free. It still happens today sometimes (we just scored another "freebie"). That rear wheel has definitely been swapped and, in fact, may not even be from a 650. It has a 42T sprocket on it which is much bigger than the stock 34T. The axle head also looks different than a 650 one, and the brake plate is totally different.
The motor and carbs may be '81. The carbs because of the pull knob choke, drain screws on the float bowls, and unpainted bodies. '82 and later carbs were painted black and had a cable operated choke. '80 carbs had a drain bolt on the bottom of the float bowl, not that screw on the side.
As mentioned, checking serial numbers will tell you for sure. The frame and engine number would match if original. The frame number is up on the steering neck, both on a sticker and stamped into the frame. The engine number is on the lower front, somewhat obstructed from view by the front motor mount .....