Got a little bit done this past weekend. Removed the rest of the rivets from the transom, sanded each rivet hole on the outside of the hull, drilled out any "whallowed" out holes to 1/4", wire brushed then sanded entire transom area to remove oxidation/corrosion, primed the entire transom area, shop vac'd and pressure washed (again) the inside of the hull. Seems like I finllay got all the gunk out of her.
Obviously the old transom board was a bit leaky. After removing all the oxidation/corrosion with a wire brush and sanding, you could see how pitted the aluminum behind the old transom board was. I sanded it down from 60 grit to 220 grit then pressure washed it, cleaned with acetone and applied 3 coats of self-etching primer.
A closer look at the pitting
After sanding, cleaning and primer. I'll probably eventually hit the floor of the hull with some sand paper and primer as well.