Geeetech i3 Pro-B X Carriage (with DWG)

I managed to wear out my X carriage on my Geeetech Pro-B and I hadn't managed to get a successful print of a spare prior.
I also find that when I download things I tend not to find a parametric file type I can easily modify. Meshes can be complex and are less accurate than parametric and many times people put up file types I'm not familiar with or are very program-specific.
So I've done a redesign and basic edit of a carriage. I took the dimensions off an STL and remade it in 123D Design. The