I live close enough to Corbin to ride to their site. My experience with them is that they will make you a "semi custom "seat. They have stock patterns for the cover of each seat and they will shave a little on the cushion to accomodate you as long as it doesn't mess with the cover that they use.
I had my vinyl covered seat reconditioned and replaced with leather. The leather is pretty thin and is not going to wear well. The vinyl wears better.
Not bad for the price, but not necessarily a top quality seat.