is there no linkage that connect the swaybar to body/chasis? whether the swaybar only mount on the torsion beam suspension?
Right - the bar stiffens the existing torsion beam, so it's mounted directly to it and not tied in to the chassis.

I put a similar 19mm rear bar on a late 1970's MK1 VW Rabbit/Golf with a similar torsion beam like the Mirage, and it made a very big difference in reduced body roll. The car felt like a go kart. But the ride suffered a bit over uneven bumps (no difference over bumps that are hit by both rear wheels at the same time).