Oh, alright. I found a mounting method in the instruction booklet for my Robart retracts that doesn't need a false rib. So, I can start cutting!

Here's what I did so far. I cut out the shape, then I'll use a hot wire to cut the wells out of the foam. The ply mounting "horse shoe" will have dowels extending through the foam and ending up against the top wing sheeting. I'll run some carbon fiber strips along the bottom wing sheeting to beef up the now weakened structure.

this thing may weigh ten pounds, but it will be a screamer, eh?