I'm not familiar with those specific models, but if the problem is that the thread on the bottom isn't the same size as the screw on the tripod, try removing that tripod screw, turning it upside-down, and screwing it back in.
There seem to be two different standard sizes for tripod heads and in my experience, the screw on the Gitzo tripods is usually double-ended, one end for each size.
Failing that, go to your local camera store and get a replacement screw. As camera equipment goes, it's a cheap and easy fix.