Ever get this figured out?
I have the same problem with my 300SD. The bottom bolt evidently sheared and left some of itself threaded into the bracket and some in the part that goes through the alternator.
While trying to pry it out, thinking that it was just stuck I ended up with a two piece bracket
The four bolts on the side of the block are easy enough to remove, but the one in front is a royal pain and it looks like removing the balancer is the only way to get access.