On the new system, the upper castings are made in such a way that the tiller arms point inwards. Therefore, there is a port upper casting, a starboard upper casting, and the lower castings are universal.
On the old system, the upper and lower castings are the same for each side, so no port / starboard differentiation. However, it's still a good idea to mark the system port vs. starboard when disassembling. This will ensure consistent helm feel since rake settings may be slightly different for one tack vs. the other, or the pivot holes in the rudders may be slightly different for each side. Also, if the tiller arms are not exactly straight, flipping the rudder system around could affect your toe in.
Greetings folks! I have the older-style castings and wanted to point out that both of my tiller tubes bend inward such that the end caps are aligned directly over the center edge of the inner strip of deck non-skid grip. Not sure if this was the way it came from the factory, but it definitely means I have a defined port- and starbord-side rudder setup on my boat. Hope this helps.