It's quite a bit of work but it isn't particularly hard work. I'm not sure on the 993, but on the 964 you can do all this w/o dropping the engine. You do have to remove all the tinware tho. Like others have said, it's a good opportunity to address other areas while you're in there.
Here's my thread showing where I did all of this stuff, and more, on my 964 earlier this year.
A photo journal of my recently completed big project - Rennlist Discussion Forums