Well, I realized after elongating the slots in the top two flanges that I didn't really need to do that after all, so I remade them (bottom two). Two more pieces for the scrap bin. Sigh.

I clamped the fore/aft ribs to the workbench and cut the top flanges off with an abrasive disc in the die grinder.

This disc started out 2" in diameter. I'm afraid it's ready for the trash.

Here are two of the four new top flanges which I bent on Clare Lutton's brake this past Tuesday. Why are there four new top flanges instead of just two? It's because I'm going to be fabricating two additional ribs for the forward structure. Per plans, there are just two stub ribs, but I'm going to change that to two full ribs in order to make the structure stronger.

I reinstalled the top skin and clamped the new flanges to the fore/aft ribs with magnets, then match drilled through the top skin.

A bit of trimming, fitting, and drilling later had the new flanges drilled to the fore/aft ribs.

Here I'm setup to use the router to cut out the new ribs.

I still need to cut out the lightening holes and make the bends, but here's one of the two new ribs.