DC these 3040's call the long Axis Y axis and Z axis is attached to X axis.!!

Craig the X axis block could easily be modified to accept open bearings then beef up the gantry with a strong plate and then drill and support the rails from behind.
This along with supported rails on the Y axis should help greatly and not cost a fortune.

Other than that then I wouldn't bother and sell the whole thing and build a far stronger machine from scratch.