Roger all that Gary...good work as well.
Here's a thought for adding the radius to a 6 or 7. Make a small lap joint inside the radius (full width), and have that sit on top of the flange at the firewall. The lap joint would contain the nutplates, and the radius itself would then be flush with the flange itself (and thus the belly of the plane).
The only issue I see with a either lap joint or the radius on top of the flange (Gary's method), is working around the rivets in the flange. I gues one could drill them out and reinstall after radius installation, or drill holes in the lap joint or radius to fit over the shop heads. How'd you do it Gary?
Bob, I worked around the flange rivets with holes in the fairing.
Nothing at the top of the fairing. It is just bent "tangent" to the firewall and fits snugly with just two 8/32 screws holding it against the firewall.
I am also not happy with the smoothness of the curve going out onto the belly and plan to rework that with an arrangement similar to what you have described. I have a small bump bluff body on the belly (only 1/2" high) but the curve does not match the radius of my firewall fairing exactly.
But ......I am encouraged by the very streamlined flow in this area indicated by oil drop tracks. Lottsa air going through here!!