Great find. Start by seeing if there are bomb shackles under the wings. If so, the model is an A-2 or higher. If you can find the rear-firing gun, a twin barrel would make it an A-5. I'm not sure what you can do to distinguish an A-2, 3, and 4 as apparently the differences were structural.
Of course, if you can find the data plate which includes the aircraft serial number and type, then you will have a full ID. I don't know where the data plate is located on the 196.