Chris,
What we need to know is if the guys are faster because you were traction rolling, or because your buggy pushed on power.
If it is pushing, remember that stiffening up the buggy will take away traction. On a sweeper, this would be counter-productive.
If it is traction-rolling, you need to loosen up the car during roll. Looser sway bars, and softer springs work in this situation as strange as it sounds (I used to race on-road) .
I feel that the buggy is slightly over-sprung stock. Maybe go one step softer all around to cure a roll.
Rather than buying a new rear sway bar, I would move the bar mounts in a little. Just be sure to measure each side and make them equal to cure a push.

BTW, I love the Kyosho T-Plate you make
How about making a stronger Ackerman bar for the EB48????