Handling 74 Duster
Alignment followed by tires and shocks. You already have the factory handling package, which is very good by the standards of the time. That's basically what my son's Dart convertible has, except it is factory big block stuff that is also supporting a big block. Ride is very good and the handling is predictable. It can be improved, but at this time it is fine for a street car.
I think this is a valuable point. "Handling" means different things to different people. If you've never driven a Miata or a Lotus or some mid-engine sports car, your benchmark for a good handling car may be very different. 442s had a reputation for being good handling muscle cars back in the day...and they were! Today, the handling of a stock 442 would be considered "scary" and despite the still-respectable power:weight, it would get out-lapped handily on a road course by a Pacifica full of screaming toddlers.
Your suggestions are 100% valid, IMO. Performance tires, performance shocks and an alignment would make for a good handling car by the 1970s standards. It would be satisfying and fun to drive. Maybe that's what the OP had in mind?
IMO, if you want an objectively good handling car (that would hang with genuine sports cars), the stock components aren't going to get you there. It seems to me that
@72bluNblu's formula is the prescribed path to making that happen...while still having something that resembles a Mopar. For example, as has been noted many times, the geometry of the stock UCAs just won't allow you to optimize caster and won't give you enough negative-camber to maintain an optimal contact patch under cornering conditions. Without bracing, the chassis isn't up to the chore of managing the huge grip potential of modern tires...and of course, chassis flex instantly spoils that carefully dialed-in alignment and adds all kinds of slop and unpleasant feedback. Eventually, you'll break windows, etc. There are lots of limitations to handling that simply weren't design priorities in the 60s when the platform came out.
Fortunately, these cars were masterfully designed. They're light weight, durable, simple, relatively well-balanced, etc. There's a reason why A-Bodies sold so well during their run...and they're objectively better than a lot of what came after them and there's huge potential to keep their performance relevant with upgraded components.
