I have an older body on frame car that rides pretty bad and loud. Its got me curious how manufacturers make newer cars ride so smooth and quiet. I’ve done some googling but not found much other than obvious, general things like “rigid construction” and “more soundproofing”. I would love to find a website that goes deeper into it.
A rigid frame helps a lot for ride quality unfortunately. A soft frame is basically another spring to flex when you hit a bump, except there’s no damper to control this motion so it can just oscillate, which produces noise and vibrations in the cabin. The stiffer the frame, the more of the bump energy goes into the damper instead (simplified statement but roughly right). That improves body control, tire control (traction), noise, and vibrations.
I don’t know how much you can stiffen an old Chevy frame but I’d start there, and use the smallest diameter wheel possible to get a lot of tire sidewall (acts as an extra soft spring preventing forces from spiking in the suspension). Further improvements can come from lighter suspension/steering components and you can always bandaid with Dynamat or other heavy insulation when you’ve run out of low hanging fruit.