Learfield and IMG College have agreed to a blockbuster merger that will combine the two marketing and media behemoths in college sports, sources say. Learfield President & CEO Greg Brown will run the merged business, which will be a 50-50 split between the two companies, sources said. The merger is expected to be finalized in the coming days, but sources say that contracts have not been signed yet and both sides are working through the final details. The move will create the most dramatic consolidation…