Install the new assembly in reverse order, putting LocTite 270 or better on the lower mounting bolt.
Fit the USM in the holes, fit the lower mount together, put that bolt in (18mm) and hand tighten. Jack up the control arm again and hand tighten the USM nuts in (13mm).
Go to the USM and tighten down the 13mm nuts and move on to the 17mm bolt. You are going to need to ViseGrip the top of the shock shaft and use an open-ended wrench on the bolt. Like so:
Make sure everything is tight, do both sides, lower the car, tighten everything again and you are done! Enjoy the new rear shocks!
For my next DIY, here's a sneak peak: