When I bought my car I found the following fax that I was able to track down to Beyer Driveline (http://www.beyerdriveline.com/), evidently they manufacture & rebuild drivelines for ECS and others. I've searched and haven't come across any other references to the 998* numbers, they may be internal. I'm thinking it may be useful to have this posted for reference.
I also came across this other driveshaft spec - I initially saved it just as a reference for the measuring points, but I suspect the original owner of my car was going to attempt to shorten an e21 driveshaft rather that shortening the 2002 driveshaft, which would require relocating the center bearing mounting bracket.
Hope this is of help to someone.
Barrett