looks more like someone forgot the captured zinc screw and instead of pulling the lower to do the job correctly, drilled out the access hole to the big hole you have.
What's missing is a plug - #7 in the parts drawing;
The plug fills the access hole for the allen bolt (#70) that secures the anode (69) covering the bolt/washer (#72/73) that needs to be removed to drop the lower unit.
Why the hole is hogged out is beyond me unless a PO was trying to drop the LU without removing the anode and #72 first because it wouldn't drop. Other that that - :noidea:
The first couple of pics show the access hole to the anode plate. Not sure what someone was needing the hole enlarged for. The 3rd looks like the prop is missing...sorry, had to say it . But the prop shaft, especially at the end looks like it has part of a hub left like maybe they had to cut the prop off and left the innards. Maybe.
I almost beat Scott, but first I searched for pitchers! LOL
BTW, Jamie - The plug isn't needed and most are missing anyway. The broken off chunk below the butcher job show the PO was trying to pry the the lower off. Wonder if he ever did manage to remove it? The anode bolt is 3/8" allen if I recall.
The guy wanted to remove the trim tab / anode and whatever tool he was using was too big, so he butchered the outdrive rather than buy the correct tool.
Now, you can't install a plug since the hole is too big.
My guess is the correct bolt was lost and they didn't want to buy the correct small head bolt and found one in there bolt can that worked. It had a larger hex head so just make the hole bigger
My guess is that he did not have a standard allen wrench. He may have only had a socket allen on a ratchet which would not allow the socket to go through the hole, so he enlarged it.
just a thought
Some zinc anode kits for Mercruiser outdrives came with a hex head bolt instead of an Allen head. If I bought a kit that had one I would reuse the allen bolt I removed. It looks like someone bored the hole wider to fit a thin walled socket or nut driver down there.
Mine has a hex head and you have to find the right socket. I can see someone getting frustrated with the wrong socket and just busting the hole bigger... The allen bolt is much better.