Note: This is the internet and any 12 year old with a smartphone can give you advice. Do your own research before spending money.
I've never done it myself, but I have had two Boxsters with the 996 throttle body. For the 74mm electronic (not cable operated) throttle I think you want this: 99660511501
The intake comes as upper and lower. The lower part holds the injectors and is metal. You will have to drill and tap holes in the heads to mount it.
While you are at it, plug this into your favorite search engine: "site:986forum.com 987 air box"
You should probably get a 996 ROW tune for your DME to get it running right.
Then figure out what exhaust manifold you want.
I have all the parts you need for the intake on my garage floor right now, but I don't plan on selling them. I can probably take pics of them if you need it.
