The bar itself doesn't care which way it twists, it just resists twisting. Mopar's T-bars are built with a 10 degree offset in them to add pre-load in their installed position so they don't bottom out as easily in jounce or rebound. The hex on both ends of the bar match on this 10 degree offset which is why front to rear is not a big deal. However, rights have a right offset, left has a left offset so mixing them side to side not only eliminates this pre-load, but puts it 10 degrees behind on the index so you would be cranking and cranking on one side to get the ride height to match, use up all your preload, and possibly snap a bar by overstressing it during suspension cycling.
