Rvich, one of my chums bought one of the seats from Vietnam, it looks just like a 'Corbin' in the photos, but in actuality is nothing like it when you see it on the bike, the rear is much too brad and the front is a bit pointy, they are cheap and even OK quality, but so ugly that my friend wont even put his on the bike as a temporary fix.
Regarding sufficient space to shorten a genuine Corbin and still be comfortable on the bike, I am 5'8" and 180 lbs. When sitting comfortably on the bike my backside does not extend to the rear bump stop of the seat, I think if you were a couple of inches longer in the arms or perhaps more generously endowed with bum-cheek padding then it would be a different story.