Put the heatsinks on the lid in the same relative position they had on the CPU board. The heatsinks are not the same. This will help ensure that they are later returned to the correct positions on the CPU board.

You can see on the heatsink at the upper right, which came from CPU A, that the thermal paste did not cover the occluding surface of the heatsink. This attests to careless pasting and assembly by the prior owner.