Mike,

nice project. That's a good system to cut the ribs. Start with two identical ply templates to sandwich the oversized balsa ribs. You can bolt them together if you bore two holes through the stack but drilling nice round holes in balsa ribs is tricky unless done with a very fast rotation bit (i.e., a Dremel). I find a satisfactory method is to clamp the stack from one side of the ribs (e.g., bottom) and then contour the top ribs to template with a band or disc sander. You then flip the clamps over and repeat for the rib tops.

If you want to make some lightening holes in the ribs, I find that a Dremel drum sander works well. Make your hole in the templates and then sand through them with the Dremel. With a little care, you end up with a nicely bored set of ribs.

Keep the photos coming!

David.