Having taken a look at the piccies you have the large white cog on back to front, the lip goes on the outer edge....looking at the piccies always helps !
With the cog repositioned (lip outermost) then it should sit further along the axle with the recess towards the motor mount. This will allow everything else to sit further along the axle curing the drivebelt alignment problem and allowing the clutch mechanism to work so should solve the "tight" running issue as well.
Let me know how you get on