I don't know what the aftermarket offers for your particular outfit - but I can offer this up.....If the rear axle roll stiffness of the vehicle becomes greater than the front, then it will become "tail happy" - loose at the limit of traction. The tail will want to come around. When driving a street car, "loose" is not fast (as per the "Days of Thunder"). The drifting cars that kids build these days have huge rear bars and skinny fronts to make this happen on purpose. Adding a rear bar that has slightly less roll stiffness than an existing front can increase the total roll stiffness of the car and give it a nice balance - hard to find the right match though if the original front bar is pretty skinny. Detroit has always errored on the side of making the front end "tight" at the traction limit - the front end "washes out" (or "pushes") in a hard turn. Increasing the front roll stiffness (alone) by using a bigger bar will keep the inside front tire in play a bit longer by resisting weight transfer to the outside tire - and the car will "transition" to its cornering attitude with much less "wallowing" around. In some cases it has been easy for guys to find used police car or station wagon front bars and it makes a cheap upgrade (they don't wear out).
I would suggest that you start with using the fatter front bar - and add an equal or smaller rear when the opportunity presents itself.