Kind of an odd one, given the D31 was an engine code, not a designation used in 1949, they were names by then, so Wayfarer, Coronet, DeLuxe, were used by then.
Basically it was the smallest and least accessorized and least expensive Dodge available, the Wayfarer was, as a business coupe, no frills, nothing fancy, including a 40percent smaller heater and rubber mats on the floor, basic, lighter than the other Dodge motor vehicle with the same D31 flathead 6 engine as the rest, so a little more pep due to the lower weight. Business coupes (I own one), have no back seat, that area is actually storage and has a flat area at the level of the top of the front seat. Shelves can be in front, or, just a larger trunk that goes all the way into the back seat area for a salesman to have a place to put his goods, sometimes a single shelf in the halfway point, not always. A twin matress can be placed in the trunk and a person can sleep in it safely and not have their feet stick out the trunk lip, haha.