My recollection (from when I removed the head for a refresh and a new head gasket) was that the exhaust manifold was pretty easy. comes apart in two pieces, and I think both slid easily out from below the car with a twist or two. Best practice is to order new nuts for the studs as they are intended to be single-use, as well as triangular gaskets where pieces mate up; the set was at least $70 from Porsche as I recall, might have been more.
Was difficult to get a torque wrench on all the nuts to re-torque (im a stickler about getting the torque as close to spec as possible), but you get the feel and can tighten the couple hard-to-reach ones without too much difficulty.
Hardest part was getting the new metal crush rings at the block to stay in place (slightly inverted with the engine in the car) while mounting the manifold pieces to the block. I think I ended up using a dot of RTV on each to temporarily "glue" them in place long enough to tighten down the nuts onto the manifold studs.
Oh, and no, I didnt have to remove any studs; luckily they were all in great shape and I dont think any of them needed to be replaced.
I believe I already had the coolant pipe removed though, since I was taking the head off.
