OMC SeaDrive 2.0L Won't Start

[bgares]

Morning Everyone! New guy here...I recently acquired an 88' V20 Steplift from my Grandfather. It has an '88 2.0L SeaDrive on it. The boat/motor were perfect for him for years. My g'mom got sick, so the boat sat for a few years (4-5). About 3 years ago, my cousin attempted to put it in the water, it started up, and ran, but after about 15 minutes just died. They parked it until I showed interest about a month ago. After reading through several threads here, I did some basic maintenance - new plugs, cleaned the stale gas out, replaced the 2 stroke oil in the VRO system, cleaned the carbs... I attempted to fire it up this yesterday, but no luck. The starter engages, motor turns, but won't turn over. I have fuel all the way to the carburetors. Now, up to this point, I've been trying to be as budget conscious as possible, as I'm not sure if the motor is good, so I don't want to dump a ton of money in it only to find it needs to be re-powered (not necessarily something I want to do). It does have dual batteries, but I've been trying to start/run it off a single battery. So, here I am, hoping for some insight on some additional items to check, or where to go next, to hopefully get this thing to fire up, and go boating! If I did it right, I've attached some pictures of the motor below. Thanks in advance for any insight!