Some rudders are buoyant, some are not. It would be a really good idea for you to find out which yours is before attempting the
installation. A "float test" in shallow
water would be a good thing to do!
If it is a sinker, then feeding a line down through the bearings and attaching it to the post would simplify the diver's job: he guides it into alignment, you pull it up. If it is a floater, then the task of getting it aligned with the bearings is more difficult, but once aligned, it will be easy to get it all the way up.
Good luck!
Jim