[bigeasy1]

Hey look! Peat Moss with fiberglass over it.Now where have I seen that before? LOL

I did my transom(also an I/O) from the inside, I removed the rub rail and cap to hull fasteners just forward of the hawse pipes,and made a cut on each gunwhale at that point.
I was able to lift the whole section off.
Cut the inner rear pane out exposing the inner transom.

Also found the same conditions as you with the vent boxes.I cant figure out why they didn't just move the vents a half inch forward when they made the hull.In order to get them back in,I had to grind down the transom thickness at the rear.

I laid up a couple layers of 1708 on the inside of the outer glass skin,before I put the new transom core(Marine Fir plywood) back in.
On the inside I laid up a couple more layers of 1708 over the new core overlapped a good distance on the inner hull sides.
It's definitely a lot more work to do it from the inside.

I used Epoxy to glue the plywood together,and vinylester on the transom layup.Anywhere else like hatches and a little bit of deck rot,I used polyester.

Good luck with the ongoing work,keep the pictures coming.