You will need the coolant crossover pipe for the ls6 manifold, as the ls1 "x" coolant pipe will not fit under the larger plenum, and 2 coolant plugs for the backs, I got mine from slp along with the manifold for I think $30. Gaskets are reusable neoprene o-ring type (buy new if you are wary of used ones) you will also need to s--t can your egr, or adapt the ls6 piece. T.B. will bolt right up, careful of the map sensor on the back of the manifold, as it is plastic, and easy to break. Have some electrical tape or vacuum tubing handy to hold up the rear bolts as you slide the manifold forward, and be ready for some sore knuckles, it's a tight fit under there!
I made a block off plate for the pass. side manifold, and removed the egr altogether, it will throw a code, but doesnt hurt anything, other than passing an emissions test.