The 12' 360cm indicates the length of the rod (approximately). The 7:3 is a rough notation for the rod's action. It means 70% of the rod is relatively stiff and 30% relatively soft (basically, it is between a mid action and a tip action rod). Unfortunately, the 7:3 notation is not standardized across manufacturers, though, so a different company's 7:3 could be much, much different than that one. I am not familiar with that rod so I cannot say how it stacks up. If you want to continue fishing the cut down fly line, the 7:3 action is probably the right one - but by know you already know it works. The rod might not work as well with a much lighter line (which would be easier to keep off the water's surface to minimize drag). That is something you would have to experiment with on your own.