New 8 inch rail was designed to replace G010-80 rail in same application.
Additional holes have been added to rail end. These two holes let you mount F12 clamp with dowel pins on rail end and prevent it from twisting. Works very nice with lens support bracket when quick high adjusting is required, when you use multiple lenses with this setup.
Second improvement is incorporating bubble levels.
You can now build panorama (http://hejnarphoto.blogspot.com/2011/04/panorama-setup-on-budget.html) replacing one G010-80 from this setup with G13-80.