Apply thermal paste
This is where things get fiddly, so you might want to do a test run before applying thermal paste just to make sure everything fits correctly and is in the right place.
Once you are ready to proceed, apply thermal paste along the exposed area of the heat pipes in the heat sink mount.
Attach the Heat Sink (L)
Carefully place the heat sink back onto the case making sure to align the 4 pillars with the holes and the slots with the front and back panels.
Replace the 4 HCS-M4x12 screws but DO NOT fully tighten them, they need to remain loose until the acrylic panels are installed in the final step
Attach Heat Sink Mount (L)
The procedure here is virtually identical to the one already performed on the right side heat sink just with the added challenge of having the other side already attached.
For ease of explanation, the images below are cutaways so that its easier to highlight the parts
Ensure good contact
Before installing the retention bar, ensure the heat sink mount is in good contact with the heat sink. It should be parallel and sitting flat against the surface of the heat sink.
As the screws securing the heat sink have not been fully tightened, there might be a gap. This is normal, the key point is to ensure the gap is even.
Fit the retention bar
Slide the retention car in from the side of the case under the retention bracket closest to the heat sink mount until it almost reaches the bracket on the other side. The bar should also be position along the heat sink mount in the slot furthest away from where the heat pipes enter.
Lock the retention bar
Bend the retention bar so that it applies pressure against the heat sink mount and is able to slice under the bracket. When installed correctly, the retention bar should be flush with both brackets
Confirm the position
When installed correctly, the retention bar will apply pressure against the heat sink mount