THE TWO most dominant forces in Barbadian calypso are set to clash on Friday night.Reigning nine-time monarch Red Plastic Bag (RPB) and seven-time king Mighty Gabby will compete along with eight other calypsonians for Crop-Over’s most prestigious crown at Kensington Oval.Yesterday the two stalwarts attended rehearsals at Combermere School, Waterford, St Michael, where they fine-tuned their four songs for the big night.