The pair of small tooth-like triangular plates on each side are (what I would call) "Footer Plates" for the Boat/Landing Craft Launching Rails: anchoring them to the hull-sides in addition to the deck. The trio of taller plates each side I would call "Bulwark Plating" for the extensive Boat Cradle rigs: each side having three uprights taller than an LCVP and supporting a second-tier set of Cradles to stack a second LCVP right over top. Again, these plates would greatly increase the structural support - tied directly into the hull sides - while also I have no doubt providing just that much more sea/weather protection for the stowed boats.
Your drawing may not sufficiently) indicate the tiny Launching Rail Footer Plates, but evidently don't show at all the tall Boat Cradle Bulwarks: however the historic pics - indeed, on most of the Buckley-derived APDs - certainly do. Including the pic of Sims in my original post. Surf NavSource and you will see them all.
On a modelling note, since all the above plates rise flush from the hull-sides, I thought to save myself some glueing and sanding by just incorporating them into the plating extensions to begin with. Wrong: from the get-go they proved far more hassle than any possible benefit. And - after all that - they may yet have to come off, anyway: turns out constructing both the pair of Launching Rails/Gantries and Boat Cradles (complete with finished LCVPs inside) as separate sub-assemblies before attaching them to the deck is beginning to look like by far the more reliable and easier approach - both for construction and painting!
By rights, I should've done some work on precisely this, today - but instead looks like all I'm gonna be able to squeeze in is this bit of yakking, on-line - Merry Christmas, everybody!