Rear suspension travel

If you want to fully limit that side to side movement, you're gonna need to go with a 4 link with a panhard or watts link. Or even a triangulated one. Other wise, you're gonna have that side to side play. and anti-roll bar aka sway bar, is not going to help with that very much if any.

The kit I have in mind is an anti-roll bar, like you would see on a 4 link. I’m not convinced the issue is side to side movement but more of a body roll. How much can our leaf spring suspensions move side to side?