Long time coming

Your B-body rear has the 4.5 bolt pattern so you'll want the same in front. A 2" drop spindle would work and you'll need the large ball joint UCA's for those. HD Rear leafs, minimal arch. Shocks? I'm not going there because everyone seems to have their favorite.

The Mopar suspension design is pretty sound and can be made to handle. (google Green Brick or get the most recent Mopar Action for a recap on what a Valiant can do with stock-based components) It's those GM and Ford guys who need to radically change their stuff. Aftermarket K's/coil overs have their place but only you can answer if you want to spend the money.