I agree you won't want port 80, but it should technically work as well.
I downloaded the latest crossftp, and when setting up the connection I chose "S3/https" and filled out the settings, and it connected fine. In the drop down, at the bottom, was also a "DreamObjects" entry, that when selected asks for the access and secret keys, then dumps the info into "S3/https" for you. That connected normal also. I lastly tried leaving it as "S3" and port 80, and it connected also. Here is a screenshot of what my settings looked like: