If you look at the metal cover plate and the hole that the crank stub protrudes through- it kind of self explains.
There is a recess formed around the exterior of that hole, this is what the flange of your plastic worm gear sits on- so the gear does not drop through and run the outer face of the oil seal.
So pump in place- metal cover plate on and screw to hold it fitted, then new worm gear dropped over crank stub, rotated as it meshes with the steel pump gear until it is fully seated.
Then greased needle bearing on crank, then clutch bell/cover or whatever you wish to refer to it as- paying CAREFUL attention to the interlocking of the drive flanges on the back of the clutch bell into the slots of the plastic worm gear- then fit the clutch.
EDIT: also, do not try to bash the clutch tight with a hammer and punch or anything similar- reassemble as tight as you can by hand- fit the bar, chain and clutch cover as per normal- start the saw as per normal, take it to WOT and slam the chain brake on.
This will cause the clutch to tighten on the crank and not shift again without the application of force.
