Let's see if this works.
O 1 O 2
O 3 O 4
O 5
O 6
These are the sheaves involved. #1 & 2 are the left and right blade sheaves, #3 & #4 are idlers (#3 is spring loaded), and #5 is the center blade drive sheave. #6 is the engine sheave. The belt goes counter clockwise, starting at sheave 6 (engine), around 2, then 1, then 5, then 3, then 4, and back to 6. Draw a diagram and connect the sheaves by drawing the belt as described above, always staying to the outside.
When installing, do #1 last as you will be able to compess the idler while installing the belt on #1.