Updating alternator - have a few questions

What are you running that you need such a large alternator?
I've never needed more than the 35A sissy alternator of about 1971 vintage.I just keep rebuilding it as necessary.Those sissys almost never need more than brushes or bearings, and you can buy one anywhere.

There's not much sense in running a 90, if you rarely use more than 10 or perhaps as much as 20.