The rack ears are apparently hard to find. Where the ears fasten to the side of the synth, they provide two sets of holes so the synth can be mounted horizontally, as seen here, or tilted forwards at about 30 degrees. Here is a close-up of the mounting:
It isn't possible to mount it vertically, and there's a reason why: the display, which is already at an angle, would be facing the floor. As you can see, some space has to be left above the TG33 in order to see the display and reach the power switch, volume knob, and data entry knob. And, unless it's near the top of the rack, you have to leave some space under it also, because it obviously overhangs whatever is below it. Nonetheless, it's still more convenient than having to find surface space for it.