The Nissan parts catalog does specify 2WD vs. 4WD option for the long block, but there are several different part numbers for each of them. The short block (engine block and rotating assembly) is the same for the KA24E in the truck from 8/89 through 97 model year, so the difference is in the head. There seems to be two different castings and the primary difference is the shape of the intake parts.
Head cast # 72P is referred to as the "wide port" design and used in the truck from 07/1992-01/1996 in CA emission certified vehicles and from 08/1994-01/1996 in Federal emission certified vehicles.
Head cast # 40F is referred to as the "narrow port" design and used in the truck from 08/1989-08/1994 Federal emission certified vehicles.
The head casting # is located at the front/left side of the head, or, a few inches to the left of the #1 cylinder spark plug hole.