I did my 98 not long ago. It had the original horizontal round top. You will find the original vent line from the throttle body to the AOS will be short for the new AOS. Even if you could service the original I'm not sure you could get a new vent line, if you were to break it. I found a number of the plastic parts in there were rather brittle and broke a few of them trying to get the AOS out.
Here's the thread on that.
http://986forum.com/forums/boxster-general-discussions/69319-oil-air-separator-vent-line-short.html