If you're not planning on doing "real truck" stuff you can soften the ride by removing a few leaves from the 3/4 ton springs. That would be a lot simpler than trying to do a swap of major components like complete spring packs, etc. Leave the main leaf in place for mounting purposes, and remove a few of the shorter, stiffer upper leaves. You can also soften the ride somewhat by using thin Teflon strips between the spring leaves to let them slip past each other more easily. Some of the "resto-modded" Cowboy Cadillacs never see a load heavier than an iced-down Yeti cooler on the way to a tailgate party- - - - -heavily padded to avoid putting scratches in the glossy-varnished Mahogany bed wood with chromed hold-down strips.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!