Preheat oven to 400. Slice the top off the head of garlic to expose the cloves. Drizzle the olive oil over the cut side of garlic, allowing it to soak into the head. Wrap tightly in foil. Roast at 400 degrees for 45 minutes. Set aside.
Combine butter, green onion, cilantro, parsley, oregano, and kosher salt in a small bowl.
Preheat grill over medium heat. Cut steak into cubes (about 2 inches cubed). Thread steak pieces and shrimp alternately onto skewers. (Note: if using wooden skewers, be sure to soak them in water for 30 minutes before threading.)
Combine salt, pepper, and next 4 ingredients (through cayenne) in a bowl. Mix well. Sprinkle over kebabs. Grill over medium-low heat about 4-5 minutes per side or until shrimp is opaque and steak has reached desired doneness.
Remove from grill and brush herbed butter over kebabs.