So, I ordered up the '04 Boxster S 550 50th Anniversary SE MAF sensor to throttle body hose, along with the "stopper" that was listed, but not shown in the diagram. The stopper was over $25 and just ended up being a plug for an unused port on the hose. IMO, it is NOT worth it if you want to do the same.
Here are a couple of pictures. In the first I have the 987 airbox, the 987 MAF sensor and 986 SE MAF sensor to throttle body hose. In the second picture I also included the 987 throttle body tee, 987 MAF sensor to tee hose, and tee to AOS tube for comparison. As you can see, I have not yet modified the airbox to fit in the 986 chassis.
While it is possible to use the 987 tee, from testing by another local shop shows that it difficult to install due to interference of the throttle body to oil cooler if clocked as on the 987, and also interference with the engine cover if you clock the throttle body so it does not hit the oil cooler. The tee also does not play nicely with the tuning if you actually connect up the vacuum operated flapper, so you would probably just use the tee without hooking up the flapper.
I plan on installing the airbox with the 986 SE plumbing after doing a baseline dyno test, then repeating the dyno testing after installing the airbox, plumbing and 986 SE tuning. The tuning will only work on an '03 or '04 S as they have the M 7.8 ECU. It is also possible to use these parts on earlier cars with stock (or whatever performance tune you have) if you sleeve the inside of the MAF housing to match the original, and use the MAF element from the original air box.
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