I used to have a 75 Newport that used double belts as a young lad. 1986? I distinctly remember getting a set of new belts and the double pulley belts were two in one package. On each belt, there is a drum number. Like a lot number. I've been told that belts are made in a wide tube, then cut in slices. I suppose you could order 50 and find two that match and send the rest back. Of course, if MB thought it was important, they would supply them in matching sets, right?