In a large bowl, combine shrimp and plums. Drizzle with 1/4 cup marinade; toss to coat. Alternately thread shrimp and plums on 4 metal or soaked wooden skewers.
On a lightly oiled rack, grill skewers, covered, over medium heat or broil 4-in. from heat until shrimp turn pink, 6-8 minutes, turning occasionally and basting frequently with remaining marinade during the last 3 minutes of cooking. Serve with green onion and, if desired, sesame seeds and lime wedges.