MTD makes many rebadged tractors including Craftsman. Search for ***craftsman tractor manual*** or ***MTD tractor manual*** and find one the looks similar. Most drive belt arrangements will be the same. My Troybilt has and idler pulley that tightens/loosens the belt. There are 4 pulleys, one on each blade drive, one on the motor and the idler. I can't picture how a 2 pulley system would work.
If you can't find a manual, you might also search parts stores for part diagrams.