From the looks it's definitely a vacuum secondary that's been converted to 4150 along with external adjustable jetting blocks. Those look like the old weber or moroso designs.
To answer your question yes it can be converted to Marine use but it won't be USCG approved. Not that it needs to be but the only conversion that can be performed is sealing the shafts and J-tubes.
Hope that sheds some light for ya.
~Ty