The rear roll center is the rear pivot ball... I know, super mysterious.
The front roll center is a function of where the angle formed by the upper and lower arms would meet, and how high that is. So making the top arm on a 1/12 car more flat would raise the front roll center.
Yes and No. The car rolls around that pivot, but it's not the rollcenter. If you raise the front pivotballs of the Links/T-Bar you will lower the rollcenter.