There's a subgear on the 650 clutch basket with 1 fewer teeth than the main gear to take up gear lash. (On a 500, it's on the primary gear, rather than the clutch.)
Press the clutch basket onto the shaft until the subgear is engaged with the primary. Rotate the basket left or right until the main and subgears align where they meet the primary gear. (You really just need to jiggle it back and forth.) Then, press the basket in until it seats against the thrust washer.