If I were going to fit that transom for a Mercruiser drive, I'd cut the vo hole out bigger, a rectangle with right angles, lay up a fiberglass plug exactly the same size, same thickness of the hull, fit the plug in the transom and glass it in, over-lay it inside with 24oz woven roven mat, then build in the transom over it. That plug Must be absolutely FLAT, it's a lot easier to get it flat on a table, rather than on the boat. The mercruiser transom mount don't allow you much tolerance to assure a good seal.
I use a chopped strand and resin mix to bond the wood together, and the bond to the hull, 2" total thickness. Get a template to cut the drive and bolt holes, the bottom of the cut-out should be (my opinion) 7" from the bottom of the hull, mine is set-up @ 9" from the bottom. I use a 2" oak block that I drilled with a drill press, same size bit, as a guide to drill the bolt holes strait thru the transom. Like Jeff said, taper the glass on the out-side of the transom glass, fill that line in with the chopped strand mix, or stranded filler.
The CV-19 is about 10" wider than the CV-16, wider floor, the seat frames from the CV-19 may not fit the CV-16 hull, I'd check that out.
