Thank you for your help! I have also contacted CoolLaboratory, and they said that
these two heat sinks are made from copper, and chips' cover is not aluminum,
so I can use their liquid metal as a TIM for CPU and GPU.
The only problem remaining that I don't know what the 3rd and 4th heat sinks are made of:
http://guide-images.ifixit.net/igi/fcEthvKik6FMxG6R.huge
http://guide-images.ifixit.net/igi/jXmoiCi3PESmiLyM.huge
So, what do you think, is it aluminum, or not?