This article on the other hand suggests that the Mac Pro will have upgradeable parts for sale once Apple has gone through all the preorders. http://support.apple.com/kb/HT6061?viewl...
You might give it a try. The only real problem looks to be the location of the two screws. Which are in the opposite side of the two boards. For the rest they seem to be identical except for the slot for flash storage.
It isn't recommended you do so, but if you want to, hold a magnet approx. 1 inch to the right of the power button. As soon as you remove the magnet, the computer will power off immediately. Do so at your own risk! I do not recommend it!