Your SE is a Series II and the SSEi is a Series I, I do not believe....and can not confirm if it will or will not. The tensioner bracketry that it sits in is different.
However you may be able to confirm it by measuring from the edge of the block to the pulley ribs on each alternator. If the measurement is different, they are not physically interchangeable. The next thing that may need to be looked into is if they are compatible connector/electronically. I believe they may be the same in this area since the PCM was the same PCM with a different Eprom being the only difference.
00 Regal GS: All kinds of cool stuff.