there you go all you need, we do them almost the same way, leave the outer grp skin, a couple of layers of 600 gram mat, 18mm ply, 2 layers of 600 with an 800/300gram combi in the middle, one more 18mm ply, and then cover it all up with a few more layers when dry, knee's and doing it the same as my learned friend
when doing an inboard you only use 2 layers of ply because there is a thickness limit, we have always only used 2 sheets and most manufacturers do the same, if your outboard has little lugs on the back plate they don't sit on the transom properly if it's to thick