SCRAPIN & PANKAKIN - Lowering Rear SUSPENsion Ideas 76 Dart Sedan
He's saying that with the front that low, there's probably not a lot of room left before the control arms hit the bump stops. Meaning you're going to bottom out a lot when you hit bump and dips. Stiffer/larger torsion bars would help. The stock ones are pretty soft, stiffer ones won't let the car bounce as much and should keep you off the bump stops ;)
BTW: I'd make VERY sure your bump stops are there. When running suspension outside the stock settings, there's all kinds of things that change. The shocks can bottom out internally and stress or punch through the shock tower. The shock towers on these cars isn't built strong enough to take a full hit of the suspension bottoming out. If you're just cruising for fun and REALLY careful about hitting things hard enough to bottom you should be OK. But if you daily drive it, or don't want to creep over every hump I'd suggest ensuring the setup is adequate for the ride height.