Here's what's approved in BSR (Boxster Spec Racing). I guess H&R is indeed on the list:
o Front: H&R 70779 OR Porsche GT3 part no. 996-343-701-90
o Rear: H&R 71779 OR Tarett Engineering 986 RSBA
The H&R front bar is not adjustable while the GT3 bar is.
Here's a link to the Boxster Racing Board:
http://www.boxcar-racing.com/forum/
I'd suggest doing some searches and research there on what their experiences are with anti-sway bars.
Here's Insite's post about his drop links:
http://boxcar-racing.com/forum/index.php?topic=448.0