Just saw this thread about Corbin seats, I haven't been here for a while..... I bought a Corbin Gunfighter on ebay, to go on my Commando with a Fastback tank, and cut it back and had the cover refitted. To make a nice tight fit to the tank I fabricated steel tabs to attach the seat to the knurled nuts.
http://www.bikepics.com/pictures/2221720/
http://www.bikepics.com/pictures/2221720/