The last photo, is taken from the hatch in the V Berth on the port side? The arrow is just forward of the portipotty recess. Yes, the garboard plug does drain from there.
Just get a hatch, and make a cut out. Many use plywood, or even the fiberglass they cut out. My current boat has aluminum 1/8" thick x 1 1/2" wide bolted to the surrounding glass, and then wooden hatches. I have re-used the cut out glass, and put in 1 x 2 wood cleats to hold the hatch in place.
Your hatches are similar to what was on the lazarett of many of the 22's. I have two of those when I replaced them with water tight hatches on the 22.
Drive on down to Hontoon gathering in next March, and I will put the two hatch covers up for auction (proceeds go to the state park for improvements).