If you get the belts to look lined up before you rotate the motor over completely twice, you'll often end up with the timing marks no longer being lined up... it has to do with the influence of the tensioner and how things work out in the end.. so it is absolutely necessary to rotate that motor over a few times before rechecking the timing marks. The reason I say to mark the teeth at that point is that if you are off after you've done this then these points give you the reference points you need to make an adjustment accurately. Marking the teeth/belt beforehand does nothing for you as the belt will not be in the same place (you'd have to rotate the motor over many many times before they'd line up again.). So it is a reference you create just before you do the final adjustment... and it is important to keep track of the crank gear against the belt as well.. hence I said to mark all 3... otherwise if you slip it off the crank gear while adjusting the upper gears you are back to being SOL as you just lost your timing relative to the crankshaft.