Cobalts diagram shows how to set up the transition slot before you put the carb on. Yours is installed. Leave it there. Back off the high idle, hook your vacuum on your distributor to a manifold vacuum source, fix your other vacuum leaks, start her up, get it warmed up, set your idle to as slow as it will run nicely and then adjust the idle mixture screws. When you turn them in and your motor slows down you'll know you're throttle plate is in the correct position with regards to the transition slot.
Cobalts diagram shows the ideal transfer slot position. Your motor might be slightly different and will need more throttle plate opening.