No. The processors themselves, both CPUs and the GPU, dont get REALLY hot. A 1/8 inch thick block of alluminum, provides quite a bit of thermal conductivity between the chips. One block for all three chips wont hurt them, as the amount of heat absorbed is already far better than if you had no block at all.
Think of it as trying to run your computer WITHOUT a heatsink and CPU fan. Gets REALLY hot, and probably smokes after a while. Now do something as simple as a passive heatsink (fanless, they are called Chipset Coolers), and see how much of a difference it makes to the operation of the processor and its life span.
I WAS going to do a test for everyone to see. First, I was going to run a graphic intensive game for 3 hours, then use a infrared thermomete to get the temperature of the processors and GPU. Then allow the unit to be powered down completely, and unplugged overnight. Then install the aluminum block the next day, run again for 3 hours, and test again, and show the difference.
Problem was the guy who I was going to borrow the thermometer from, backed out on me for some reason.