Wow, that?s looking really good! I am really pleasantly surprised at how good things are looking. The only real suggestion I would make is for the sister ribs, it will really be easier, faster, and actually stronger if you put the sisters next to where the original ribs were, and overlap the sisters and the original ribs by as much as possible. I would say by at least 6? wherever you can. This gives you the advantage of not having to measure and cut their lengths precisely, and also avoids that butt joint (of which you are correct would need additional strengthening).
Not a bad idea to use some adhesive on the sisters, however they really should be screwed from underneath too (as originally done). Don?t worry about those original screw holes not being aligned with the sisters, they can be filled and cause no problems. Something to keep in mind about using an adhesive between the sister ribs and the bottom, any adhesive will hold only as well as the paint is adhered to the plywood. So either make sure the paint is well stuck, or scrape it off to bare wood. (I like something like a Sikaflex ?1a? or ?291? for something like this.)
You will need some way to tie the rib ends to the keel. I have been thinking the easiest way would be either some wood ?horseshoe? shaped pieces, on the side of the keel, one at each rib end and ?capturing? each rib end, or maybe a long thin strip of wood (oak) along the side of the keel with notches for each rib end. ? Does that make sense?
That is good news about working the hook out of the bottom. It sounds like you are making good progress.
sort of crude, but this is what I had in mind for the sister ribs (the sisters being in green).
And husband has been working back near the transom. He's pretty much got it flat back there. Gonna go a little bit more on that. Here are a few pictures of my clean up on the front and of the white oak we got cut today for repairs. 
