If your son is bringing 60lbs of books I recommend he go back through them and make sure he actually needs to take them. All ships will have pretty much any book a deckie will need, minus just a few.
Anything having to do with celestial navigation can be left behind.
If he still wants to take a ton of the books I recommend that he take them with him on the plane. The reason for this is how easy mail gets lost when being sent to ships. With a "home-based" MSC ship that doesn't travel to different ports very often it's a bit easier, but can still be a pain. If you still decide to ship I recommend your son find out the APO address for the ship if you want to mail it to him and that way you will only pay shipping to the port of exit instead of all the way to Japan. He could find this by calling MSC or probably even looking online.