Maybe I can be of help!
You may find that the shroud plate is made up in the following way in that you will have a longish plate as in the picture but below the deck and on the inside face of the hull the plate has two stainless cross plates welded to it.
This is glassed into the hull before the deck is put on and then the deck has two slots in it for the plates to come through when the deck is bonded to the hull.
Then the cover plate is put on the plates too cover the slots and a screw or bolt is put through the gunwale and plate and bolted on the inside of the gunwale moulding.
You can feel inside the hull a slight raised area under which are the plates.
Your job!! If you choose to accept it?? is to grind away the crovering glassfibre and if you can still get the plates( try Ian Porter) reglass them in!! Just Like That!!
Or you can use the plates shown in the picture which are actually two different length plates and bolt them through the hull.Remembering that when put in the same line as the old plates you will have to drill through the old stainless plates.