Exactly this ^^
You should have not problem mapping and Amiga HD to the "real" OSX drive (I have done the same and in fact use a Dropbox folder so that my projects are constantly backed up)
.... However , you'd have to constantly covert to/from ascii within Amos itself if you want to type in code using an OS X editor.
Even then, you won't be able to take advantage of the Amos tokeniser feature (that helps greatly in cleaning up syntax etc)