Let me start by saying I have a very cut up Boxster and a buddy has a 911 rear end sitting around that I could get a deal on... Now for the question: Could you make a 911 dual A-arm rear suspension work on a Boxster which has a McPherson suspension. The lower half of the suspension is the same but the Boxster does not have the upper connection points for the top two arms (links). These would have to be welded on with incredible accuracy or the 911 subframe would have to be adapted and used. Both subframes seem to bolt to the car with bolts that are at least close to the same location and the cross supports appear to be in the same location. An interesting observation: the 996 uses rubber subframe mounts and the Boxster has solid metal mounts. Not sure why.
Lets get out of the way that any improvement would be minimal and there is no good reason to do this. This is typically what I say when starting all my "modifications", and if you've seen my other threads you know I have a high pain threshold for horrible projects with a lot of fab work.
Step 2: how could you make a rear dual A arm suspension work on the front of a boxster....
Here's some terrible shots of a 996 setup and subframe
Here are some equally horribly 986 shots
