20SF transom thickness

[FLexpat]

The biggest concerns with a 2" transom core are that the thicker transom may cause other parts to not fit like a cap with stern wells, motor well, and some through transom fittings or transom mounted stuff like steering components.
For some motors (and most I/Os) the max transom thickness is 2.25"; with a 2" core where you have bonding between the two 1" layers plus bonding to one old skin plus one new skin, it is real easy to get way too thick. If you plan ahead well you can grind out the areas that need to be thinner but Coosa is made with mat embedded in both sides so you probably need to make up for that in the ground out areas. Wear Tyvek and a good respirator plus glasses/mask when grinding or shaping Coosa - I speak from painful experience there.

a few pounds of extra weight from the thicker core is trivial

Have fun!