Now that you've sorted the need for a spacer beneath the chiptray for the lathe, how about this for a suggestion for siting the milling machine.
It looks as if your benches are on castors, and have adjustable feet, so:
1) Move the Mill head to the bottom of the column and clamp it there, firmly.
2) Rig a shearlegs and , with a sling around the head of the Mill, hoist it as high as possible with the chainblock.
3) Roll the bench under the Mill whilst it is in mid air
4) Lower the Mill onto the bench, and bolt it down.
5) Remove the sling, chainblock and shearlegs.
6) Roll the bench to where you want to site it, and screw down the adjustable feet.
Plug in and play!
Howard