Iggy,
Your referral to
www.Yachtd.com may turn out to be fruitful. I've contacted them, and Korolev, a support engineer, has recommended a Fox Marine PCM555 gateway, after informing me that my Mercury ECM is: "an old Motorola PCM555 controller variant." Geez!!!
So...it looks like I'll be removing the cable that runs from my ECM diagnostic connection to my N2K backbone, removing the Smart Craft unit, and replacing that set-up with this one, from the engine to the N2K backbone.
I'm awaiting some clarification on the installation and application before I order the product. This looks encouraging.
Thank you so much for your guidance!
Dan