One year on, some problems persist, but KC’s Streetcar has boosted business along the line. Lunch customers lined up for ribs, brisket and other barbecue specialties on a recent weekday at Plowboys Barbeque, a new landmark along the streetcar line in downtown Kansas City. Plowboys opened at Main Street and Petticoat Lane in January 2014 and moved into a larger space at 12th and Main in October of last year,…