Here is a recent discussion on the 996. What needs to be done is discussed in this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/761947-993-vs-996-prices.html
In regards to whether or not you will fit comfortably, here is a clip with Clarkson in a 996. I think he is 6'6" or so.
Porsche 911 Turbo car review - Top Gear - BBC - YouTube