Ok.....so I think that I have this about figured out now.
In doing research on the web, it would seem that these bellows are the same as the 'GT' bellows which I have found dimensions for length of 360mm. That got me to go back and measure the 45S again. Although I measured the rail as 17", the distance between the front and rear standards where the bellow frames attach is only 15" or 380mm. So I am thinking that the 360mm measurement must be correct.
Thanks again John for your help,