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.

Absolutely not. Money no object, and assuming you’re only picking from factory options, the Dakar is the one to get. Less delicate, more versatile, and still a head-turner.

Unless it overheated, an S58’s not going to care about 6-7000rpm at low load for 10 minutes. We regularly run these things on track, to redline, under full load, with G-forces compromising the oil supply, for 20 minutes.