Here's something I see missing with the seats/belts anchored together gig. It's called inertial loading. Seat belts are all about being respectful of Newton's first law which states in short 'objects in motion tend to stay in motion'.

My bench seat weighs 50 lbs. I weigh 320 lb. If I anchor myself to the bench seat and expect it not to fail then the seat mounts better be able to handle the sudden forces associated with deccelerating 370 lb. If the seat is anchored by itself then you can see these fundamental forces are reduced a factor of 7.4.

That said I too like the idea of a plate beneath the floor on glass rods to spread the seat load points out, but I'll make mine aluminum. That will more than hold the seat for any minor fender benders that could be survivable in a glass '32. I still like anchoring my big butt to the frame though ..............

Kitz