BQ

I can post only 2 at a time. More will time out.

I use a contour gauge to get the top of the rib shape and trace it onto the top of the pattern, in this case foam sheet

I use 1/16" foam from my kids craft box to get a rough shape of the rib. One can use card stock as well. It is easy to place up against the original ribs. After you get a shape you're happy with, trace it onto the wood you will use for the rib. And rough cut a rib.