Some useful information i ran across while looking for ways to identify a 4.0L for DIYJ. The casting number is cast into the head, and found on the drivers side. The year ranges follow:

Year............Casting No
1987-90......53005535 (8933002665)     2686
1991-95......53008405                  7120
1996-98......53020569                  0630
1999-04......53010449                  0331