flaps started out johnson, electric optional then stock, original a & b variants were known as super Rs 200.. but often called sierras'
early didn't have rear pax door & 28v came in at the end etc..
+ another yuuuuge rear door, some also have 6 seats
http://indyairsales.com/wp-content/uploads/2017/05/N9199S-3.jpg
http://indyairsales.com/1975-beech-sierra-n9199s/