This afternoon I otted in the forward seat attach flange. To ensure that the seat rails eventually fit flat I clamped wood strips to the aft seat mount flange, placed seven bid spacers under the forward parts of the strips, and clamped the forward flange to the strips, then to the forward seat flange bulkhead. So when I place the seven bid reinforcement on top of the flange, it should be at the precise height of the aft flange. Hopefully.