Haven't had to touch the alternator on my m3 but I took it out multiple times from my 330.
be patient getting it out, it takes a little wiggling. I would personally take the whole fan shroud off to make room to work. Would imagine it would be tricky getting the alternator out otherwise .
2001 330ci - 117xxx (sold)
2001 M3 - 90xxx
1989 325i - 2??,???