IS IT VERY HARD TO DO. ANY SPECIAL TOOLS?
TIA
OOB

Many people swear its a PITA, but AK builders do it pretty often on the crappy imported romanian riffle (either fixing canted sights/gas block or replacing a neutered lug).  The method most common is to drill the hole larger and use larger pins so that the pin journal doesnt sit half in the new and old grooves and allow it to move.  with taper pins Im not sure how the procedure would go, but you could always use steel dowel rod.  If your planning on using taper pins again, be aware that you WILL NEED a taper reamer.  If your mechanically inclined I would say it wouldnt be hard, but this isnt for the standard hobby builder.  

I've changed four of 'em and only had a problem with one. I had to put the barrels in the freezer overnight before I could knock out the pins. Be sure to to punch from the small tapered side (muzzle to your right and the tower pointing at ya). I drilled a hole in a piece of hard nylon block for the pin to drop through. Hockey pucks are a favorite 'round here. BTW, had to really apply hammer force in all cases. Once broke free, no problem.

Good luck on matching a new gas block with what ya got. The holes need to exactly match or you're just whizzing in the wind. On a mismatch some folk drill and tap for set screws. Not my cup of tea...

Hope this helps. KNOCK 'EM OUT!