I made the 4 F-916C spacers out of some stock bar of AB4-125 material.

These spacers are inserted between the inboard seat ribs and the F705B center section bar. At these stations, there is no doubler bar and these spacers make up for it.

To make the center hole, used the center punch to make the location, drilled first with smaller drills and finally used the #30 reamer to make a pefect hole.

Continued then straightening flanges and fluting the remaining seat ribs.

The baggage area ribs are almost straight and need only little tweaking.

Installed all of them on the center bottom skin.

Then turned the assembly around to be able to matchdrill in an easier way.
At that point you realise... that's a shitload of clecoes.