A piece of stainless steel plate has been added under the lower bolts (needed to get longer bolts!). On another variation of the modification this plate is eliminated. Instead a hole is drilled in the end of the existing chainplate to receive the turnbuckle toggle & the wood block has a clearance slot routed.
Note the access port in the settee back - this was to allow passing in the threaded rod & strong back (it is aft of the WC bulkhead on both sides)