Well here goes... Aluminium frame router design

[CharlieRam]

Maybe i am being thick but i cant see how flipping the rails will introduce vibration, looking at the conventional method then the spindle is mounted away/lower from the bearing blocks whereas my design is a constant length of zero from the base of the spindle clamp to the bottom of the bearing block. Is it the spindle clamp causing the issue or is the spindle too low in the clamp? How low can the spindle be in its holder?

Also think i may use a plate across the back of the machine like you suggest, I suppose one open end is enough if I need any overhang
Cheers