On the under side of the front side heatsink we need to add a small coating of thermal compound to the little recess which the heatpipe fits into. When the assembly is screwed into place the thermal compound on the base assembly should be enough to fill out any of the surrounding spaces, but you could always add a very thin coating here as well in the immediate area of those eight screw holes.

The top side heatsink goes on over the heatpipe so it locks into place. It can be slid around for a few seconds to help spread around the thermal compound but ultimately we need to align those holes with the ones on the base assembly.