don't have your handbrake on, then you can't remove the drum.
Overview of the rear brake:
My number 3 (see pic) was missing when I removed my rear brake drum !
Not fully sure about the balance, but it needs to be equal on both wheels.
I just did it with trial and error, adjusted the screw on 4a, put the drum and the wheel on, and applied force with my hands for a second to rotate the wheel. I repeated this until I was only able to turn one full circle.
Hope this helps, and if someone else got any better advise