Good point of the double plate for easier adjustment.

If you want a stronger machine...
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Regarding the length of the X axes screws and the overall length of the machine I do not see why you need the frame longer than the linear rails. If you lower the ballnut mount with a spacer and move it to the back (closer to the motor) you can shorten the screw at front by at least 10 cm, having the end blocks going under the gantry base plate.