Not the best pic but you can easily see the how the KB bracket over lays and uses the tensioner mounting bolt locations.
http://www.bigkid.ls2.com/KB/P1010034.JPG

 

The idler bracket will need to be shimmed because the standoff of the MagnaCharger Tensioner is different. You may also run into an issue of the tensioner arm actually contacting the idler bracket.

 

I think you may be right. I was looking at everything this weekend and once I get the 100mm idlers on, the longer arm of the new tensioner may be too long and contact the idler or be so close that it creats a really sharp angle for the belt to travel.