the 1.81 is the gear ratio.
The 0L number is the serial number and there is nothing there to decode, it's just the Mercruiser ID number. This number is also used for ordering parts. That way you are sure of getting the proper parts from the Merc dealer.
You give him that 0L number, he punches it in the computer and the proper parts book opens.
You can do the same at Mercruiser Parts Express
