That looks great!
It is interesting to see another TAKE
on the same challenge from a fellow engineer.
My goal was to put the flange on the outside for as little intrusion into the airbox as possible (to minimize turbulence). I used 2 gaskets, cap screws with nuts and lock washers, no sealant. My flange started off as a "cheap plastic" Spectre flange from Advance. I turned it, shaved it, drilled new bolt holes, and painted it.
Pictures "under the knife":
The cone filter coupling started life as a real-estate info tube from Home Depot!