Torsion bars

Shocks going soft are way more likely than a torsion bar, as it's hard spring steel.
Replace the shocks first and the ride will probably have improved enough again. You can always turn up the torsion bars a bit.
Better (more expensive) shocks do a better job of controlling the suspension movements.

And yes, the cars' springs were setup kinda soft in those days.
It's popular these days to step up the springrates of the bars to almost what you'd expect to find in a modernday car.