Zachmccool, You start with a plywood ring spaced just behind the spinner. The spinner should be about 2 1/2" to get a good flow into the fuse. Build up slats from the fuse to the ring with balsa, about 1/2" square slats work great. Work your way around the cowl, fitting the pieces in as you go. Make sure you only tack glue a couple of the slats to the firewall. When you finish with the balsa slats, sand it to shape, then cut it off. sand a bit more (for the thickness of the FG). Then FG the whole mess (outside?) Hope this helps