Yesterday I received my (NOS?) K40. I bought the classic version with analog amp-meter, because it was cheaper and the digital power control from the upgrade version had some negative comments.
To my surprise, it came with a functional Chassis-GND connector and has a Lid-switch to interrupt the laser, when Lid is open. Those were two items on my todo-list I could check immediately.
But best of all is the fact, that it came with a real 700mm tube, manufactured march 2021. 🎆
I read that most K40 only have a 650mm tube, so it was an extra bonus for less money.

To answer my initial question, the room below the laser table is ~80mm, just not enough for big coffee mugs I'm afraid.
I've read about different lenses with much shorter focal point (1.5" vs. default 2") and there's also a chance to reduce focal length 4mm by turning the 2" lens around, so it's a close race.
I might just cut out the bottom at some place if need be.