[ryanroo]

the deciding factor will always be spring rate. if you get a longer spring, with more rate, it will still be a little rough. the newer trucks all use comparably longer springs with less rate, but with a substantial overload. the overload is used with very little load added. as Tim said, with no additional consideration it will have more roll or sway if you get a softer spring. usually lift springs are stiffer and will make the ride a little more bouncy, unless the springs are chosen with a lower rate.

shocks can also be a factor. to much compression valving and they will be bouncy. to little and they will be wallowy. to much rebound valving and they will feel rough, to little and it will be boingy

to keep a leaf spring and get a nice ride, i would say longer spring are necessary and use a helper bag to keep the capacity up.

there are an huge number of resources for four link design. it is very involved to do, but there is a lot of info available.

mine is as you said, bags and links. should give a super ride, way increased capacity and if i did it right(i think i did) there will be less body roll than a stock truck, vintage or modern. and have better handling manners all around.