www.tinboats.net it's a forum like this but all about aluminum boats. You can find anything you want on there and a lot have videos while the work is taking place.
You might PM catman529 or try a search. He replaced the transom in his jonboat a year or so ago with a piece of white oak I gave him and he had a post with pictures showing him resurrecting his old jonboat.
I replaced one a few years ago. I used treated 5/4 decking. I cut it to fit then coated it with fiberglass. I happened to have a sheet of 1/4 aluminum which I cut to fit across the top inside and out with a 6 inch wide piece calked and screwed on. Works great
As an Amazon Associate we earn from qualifying purchases. Product prices and availability are accurate as of the date/time indicated and are subject to change.