I would say standard right hand threads also. Be sure to take the mechanical pickup apart on the left side. Unless the PO kept in good operating condition, there's a good chance the internals on that are caked up with a mix of grease and dirt. They are a pretty simple dog type mechanism, but a mix of dirt and grease combined can make them sticky, and not work properly.
If you have the room to run, those old pull type plows do a good job, and are fun to plow with, as long as it has some good shares on them. Looks like it could use some coulter's.