The III's back removes with four latches. The IV's back removes with a single lever lock, as shown on this camera. Generally III's have grey leather, IV's have tan leather as shown. IV's were made from 1956 to 1964. These make great shooters, but personally I advise passing up cameras in not so great shape, unless you are getting a great price.
Repairs are likely to be expensive.
They could also be ordered with Voigtlander lenses, including the famous Apo-Lanthars. Some cameras left the factory with sheet film holders. The original Linhof sheet film holders were individually boxed and each holder was numbered at the factory with a complete set being 12 exposures. Shown in left pic is the mount for the anatomical grip. Closeup on right shows one of the four knobs which lock the back movements.