I have just been out to my old block and had a look. The upper shaft timing mark is at 12 o'clock, therefore the keyway cannot also be at 12, it has to be slightly counterclockwise (10 or 11). You appear to be right regards the picture in the PWM - it has been rotated clockwise a few degrees. If you look at the Clarks diagram - that shows a more acute angle between the shafts and is much closer to the actual reality of a fitted engine. The rule is the keyways must always be up, but they cannot be at exactly 12. However, the notch on the upper sprocket will be.
Yes, some later sprockets did not have a U stamped on them, they used the thin metal cover with holes in to identify the sprockets. On the upper one the O appears in a nice large round notch and two pin ways are also clear. On the lower the O appears in a rectangular slot and the other two pin ways are clear.
Here is a (grainy) photo taken from the PWM. It show the upper shaft, as you can see the O (visible in its nice round notch) is at about 11.
Hope this helps.
Have a read of Clarks ENG-08, they discuss the sprocket id issue and the problems that can occur due to Porsche not stamping U on them..