I haven't done this myself but this is not the first time I have heard of
this.  I would remove the steel water line that is in the way of getting to
the bolts.  Remove the alternator and bracket completely.  If there is any of
the bolt still sticking out from the block you might be able to start it
loosening by using a small chisel and tapping it in a counter-clockwise
direction.  The bolts shouldn't be in there tight.
Let us know how you make out.
Ken Wilford
Van-Again
John 3:16