The ornamental design for a differential having externally mounted plenum, as shown and described.
FIG. 1 is a side front perspective view of a differential having externally mounted plenum showing the new design.
FIG. 2 is a front perspective view of the differential having externally mounted plenum.
FIG. 3 is a first side elevation view of the differential having externally mounted plenum.
FIG. 4 is a second side elevation view of the differential having externally mounted plenum.
FIG. 5 is a bottom plan view of the differential having externally mounted plenum.
FIG. 6 is a front elevation view of the differential having externally mounted plenum; and,
FIG. 7 is a rear elevation view of the differential having externally mounted plenum.
Any portion of the differential having externally mounted plenum shown in broken lines is for the purpose of illustrating environmental structure and forms no part of the claimed design.