how hard
You will have to remove the headers, in your case for the turbo, you will have to get them out of the engine bay so you have room to get the head out of the car.
I think with yourset up it would be a little more indepth than a normal NA car, but far from impossible. I would set out a weekend to get it done right (taking your time)
If you are going to the hassle of pulling the heads, consider buying new heads?
Read up on this to get a general idea of what is required....
http://ls1howto.com/index.php?article=2

