You need the Rinda tool that is made for Mercruiser, I have seen them on ebay, but it could be expensive for a one of use, also you need the correct connector for your engine, marine engines don't use an OBDII port as that is an automotive system.
I still have Rinda scan tool gathering dust, I was going to put on eBay as it didn't sell when I tried via the forum, I don't have the cable for your engine but these can be purchased from Rinda and they are very cheap, if you want it make me an offer, saves all the hassle with import charges etc