Skin on frame sailboat stiffness

Your gunnels are going to straighten out, causing the boat to hog.
Your "substantial" keel will do the same. Unless you laminate the gunnel in two pieces on the mold (split on a horizontal plane) and the keel is laminated (split on a horizontal plane).

I also want to know the progress.

 

I just noticed the picture with triangular reinforcement blocks for the bulkhead to stringers.
Works like a champ.
I did it on a kayak, it was the most OCD thing I have ever done.
Took a huge amount of time, because the joints are not perfect 90 degree intersections like you illustrate.
Everyone had to be individually cut to fit, I doubt that there were more than 8 where 90 degree stock worked.
Even then, to make the ends fit neatly, each end had to be filed to fit, sanded, epoxied on the outside (if you choose that kind of finish), and sanded again.

Never, ever, again in my life - but I did like how it looked!

The triangular blocks do substantially reinforce the joint, but on SOF most of the deflection comes from the long lengths of unsuported frame.

Using an epoxy fillet works just as well for joint stiffness and is much easier, but you need to work neat to avoid excessive work or ugly joints.