Hi Doug,
I hate to bring up this subject since it always meets with mixed emotions here on the list, but when I had my generator replaced with a GM alternator on my '59 Imperial, my mechanic was able to easily create a bracket to hold it. I still have the old pieces, but prefer to save them in case I want to put the generator back on in the future. I doubt the '59 would work on a '58 due to the engine difference.
Bill '59 Crown