Trim fat from meat. Stir together mustard, honey, curry powder, and chives. Brush about 1 tablespoon of the mustard mixture on roast. Insert a meat thermometer near the center of the roast.
For sauce, mix the remaining mustard mixture with sour cream; cover and chill.
Arrange preheated coals around a drip pan in a covered grill. Test for medium-low heat above pan. Place roast on grill over drip pan. Cover and grill for 1-1/2 to 2 hours or until desired doneness (145 degrees F for medium-rare, 160 degrees F. for medium doneness). Remove roast from grill and cover with foil. Let stand 15 minutes before slicing. Serve with sauce and, if desired, snipped chives. Makes 12 servings.