Plate and small holes on Port Aft Gunwale
After looking at your videos of this H733, it appears that this was originally a vessel that was equipped with a Diver Door and the appropriate tube set to match. The original tubes were replaced with a standard set by wing that no longer gave access to the diver door. Looks as if someone may have had a bracket there beneath the gunwale portion of the old door.
Good looking boat overall and with a little TLC will make a fine setup for someone.