How would you fasten back to back carriages?

[CharlieRam]

I am changing my gantry and Z plate design, I am now trying to put the rails on the front face of the gantry instead of top/bottom.
The problem is now that the carriages for the Z plate and Gantry are in conflicting positions, How would I be able to fix them at opposites?
The only way I can think is by attaching the carriages to a plate with a flange and bolting through the flange onto the existing plate but this will increase the thickness of the assembly, any ideas?
If I move the Z plate carriages up by 44m that will allow me to bolt both carriages but it will also mean the cutter will be 44mm further away from the bottom of the bearing reducing stiffness!