if you read the thread i attached previously, mrmiatanut gives a bit of info, including an invite to visit:
"Its a 99 A8 4.2 V8 engine run by AEM fuel injection. The tune still needs a little work, I haven't had a chance to put it on a dyno yet, hopefully in the next couple weeks. Everything custom made. Motor mounts, transmission mounts, wiring harness, cooling system, flywheel and clutch, etc. If you're ever in MS stop by and I'd be glad to show it to you."
the thread also has a lot of dialogue on the various transmissions that will work.
here is an interesting thread:
http://m.modmotortech.com/forums/showthread.php?t=1240791
it's an ls into a 996, but what is interesting is two things:
1) the dme conversion doesn't look that difficult; he uses the porche dme to run the car and the ls dme to run the engine, and just does a bit of cross-over where the porsche dme needs engine info (speed, rpm, etc.).
2) the guy from renegade hybrids chips in near the end of the thread and gets asked two quesions (about the two telling ommissions from his web page on is 996/ls conversion kit): do you have to cut the frame, and how do you handle the electronics. apparently you DO have to cut the frame on his 996 conversion, and apparently he was having trouble with the electronics on his kit. so, perhaps this explains the lack of uptake on his 996 kit, and the lack of a boxster kit.