I don't think that middle slot is for a belt; I think it's just spacing.

 

I agree with you on that.

 

yeah i don't see three pulley's the third pulley is removable and attaches to the balance with 4 bolts i think it should be simple as to just adding that third belt, but if it works in that position why change it lol.

 

The cool thing about belts for transmitting power is how forgiving they are about mis-alignment.