Not to rain on anyones parade because it's been hashed out here many times, but in a word, YES, the factory, and at no extra charge to anyone that owns a muscle era Mopar.
Better suspension parameters than contemporary offerings from ANYONE ELSE, including the much touted MustangII (actually very, very, similar and why not, Ford designers had the smarts to copy a good thing, fourteen years after the fact later).
You want to really improve the handling of these cars? Try minor reinforcement of the basic structure, proper selection upgraded parts (both factory and aftermarket) paying close attention to spring, shock, steering, and stabilizer rates, and upgrading of wheels, tires, and brakes, then design and install a compatible independent rear suspension because, arguably, that's where redesigning of the suspension would make the greatest change, mostly because IRS lets you radically reduce the the rear unsprung weight (if you want to be really radical, spring said IRS with torsion bars). You could end up with something very nearly the equal of virtually any modern ultra high performance car.
It's all been done before people, just look at what the factory was doing in the 60's and 70's if you need inspiration.
I find it amazing how people think they need to throw the baby out with the bath water when thinking just a little outside the box (and maybe a custom built set of headers) when packaging the engine and it's components would get the job done.
