How do I create this in AI?

I've created this thing in Fusion 360, which will be 3D printed.  Two of them will slide over the objective lenses of a pair of binoculars.

I need to laser-cut a piece of film to cover the top, fitting around those crenelations.  I've used AI for years, but I'm still basically a novice, and, try as I might, I can't figure out how to come up with a drawing that works (must be a PDF made from continuous lines for my laser-cutter).  I can output a DWG from Fusion 360 that's close:

I need to delete some of those arcs, though, so it looks like this:

but the arcs come through as complete circles (the inner one and the outer one), even after ungrouping, so I can't just select a part and delete it.  It seems like it should be easy to create from scratch in AI, but I can't figure out how.  I created the figure above initially using the Shape Builder tool, but the line segments aren't individually selectable, so it ended up kind of being a mess that I cleaned up in Photoshop, and the result (above) was a bitmap which isn't ideal for cutting on my laser-cutter.  I can do it if I have to, but I'd prefer to vector cut rather than raster.

Any tips would be greatly appreciated.