An A body's shorter wheelbase is necessarily going to give a bit choppier ride than a B body. That said, what suspension do you have now? Factory soft, factory HD, aftermarket? Kinda hard to recommend without that info.
Roads make a difference, too. I never had a problem with the way my 65 Barracuda rode until I drove it to the Mopar Nats a few years back, then visited family in and around Eaton, Ohio. Holy s---t, on those frost heaved back country roads, bounce, bounce, bounce. Doesn't do that down here.
