So your car has no sway bar on the rear at all? If that's the case why not bolt on a factory (or factory type aftermarket) gbody sway bar? They bolt up to the lower trailing arms so the exhaust won't be an issue.
1980 4-door Malibu Classic
-355 10.5:1, worked over L82 Corvette 202 heads, 274 Energizer hydraulic cam, MSD Streetfire distributor and wires, Edelbrock 625?cfm carb (temporary), shorty headers, 2 1/2" (or maybe even 2") full duels (2 1/2" to come this summer)
-B&M TH350 with 2400 stall
-7.5 with 4.11 limited slip, rebuild drum to drum with support cover
-15" steelies with 24 1/5" tires
-Edelbrock boxed lowers, double adjustable uppers, anti-hop bars, and tubular braces
-jounce bars, GP bar (not installed yet), rad support braces, fender to support braces