Mstennes - the Galil has nothing in common with the above AK 47 build notes. The Galil has a milled receiver and the barrel just threads right in, no pins involved.
Shotgun News just did a two-part article on building a Galil that is very informative.
I just recently changed out the barrel on my Galil and it was a very easy process. If you have to remove the old barrel first, it helps to heat the receiver first. The barrel flats are 20mm and a breaker bar is helpful. Reinstalling the barrel is just as easy, and you shouldn't need more than 100-125 ft/lbs of torque.
The gas block is pined to the barrel. A press is helpful but not necessary. A non-marring mallet or a block of wood can be used to remove/install the gas block. I have read that it is possible to put too much stress on the barrel with a press if one is not careful.
Good luck.