No drawings done yet I'm afraid, it's just an idea in my head at the mo., based on what I've learned from making my little machine. I can tell you that it will have a pretty massive "extrusion" for the gantry though (likely 200 x 130mm), and will use the same dual ballscrew Z-axis arrangement to minimise the offset between the gantry and the spindle - even more important in this arrangement if you want both spindles to be able to cover a decent working area whilst keeping length to a minimum.