There is a small washer that fits on the crankshaft the keeps the oil pump worm gear away from the crankcase seal. I do not see it in your pictures?
After you install the pump, and set the worm gear into place, when you install the clutch drum with the rim sprocket, the drum must be fitted to the worm . . .
There are pieces of the drum that mesh within the plastic worm gear. If you install the clutch drum without working it into the drive mechanism of the worm gear, everything will be in a bind and the clutch will turn all the time.
The big washer goes between the clutch drum and the clutch spider before you screw the spider on. The writing and the wrench flats go towards the outside of the clutch