We went the route of making a base they fit into - and that fits into the cutout on the table. The machine can not be lowered though - The bases are all the same exterior, but they are different interior so they fit each specific machine, and the machine is hinged into the base so it can be tipped back for oiling.
The good part, when placed on the shelf, the base is still attached to the machine.
Though so far, DH has only made one . . . but we've got the plans made. They are actually made from 2x4's and routered out for the different machines. This way we've got a lot of wood to work with. Some will have a lot routered out and some will have very little. And we may even have some that need wood added as they are quite narrow.
I also plan on doing something similar with a hand crank - make a wood part that attaches to the base that the handcrank mounts to.
Here is where the "idea" came from. This table is made to accept the base of a bentwood case machine.
and when you take the machine out, the tray that it sits on can be lifted and blocks can be rotated that hold it in the upright position.