Shawano may be out of business for some time, but about 8 of their conversions are on the FAA database. You might try checking the FAA STC database for Shawano mods. Shawano is also a County, a Town and a Lake in Wisconsin. I have fished somewhat near there years ago in the late 1950s.
I can't comment on your cowl question, and the remarkable N233N is not my Beaver, unfortunately.
My various Beaver photos here show several common mods-wing fences, tail fins, turbo conversions, window mods, etc.
I did charter one in Alaska as copilot in N4444Z, of Rust's. See my photos here of various Beavers under DeHavilland in production aircraft and under Lake Hood SPB and Lake Hood Strip Z41 in my Airports section.