You were not clear about what type of springs are used on the rear end. The 4-leaf buggy spring up front should be about right; the poor ride qualities are mostly generated by the rear suspension (you sit closer to the rear).

If you have the classic Model-T or Model-A double-arched buggy spring in the rear, then you have some of the coolest looking but poorest riding suspension ever devised by a human being. You can try removing a leaf or two to soften the ride, but that configuration is just naturally stiff because the spring leaves are in a constant bind against one another.

If you have coil springs back there, try opting for softer rate springs and softer shocks. I have had excellent success using the REAR coils out of mid-80's Ford Escorts (not from a station wagon - they're too heavy duty) and standard duty FRONT shocks (not gas type) from mid-70's Pinto. Another good spring is the progressive wound type from the REAR of a Chevette, but they are just a little taller & may not fit.

If you have coilovers on the rear they may be too stiff for your application. Different springs are available for them from several different parts houses (Speedway Motors, Summit, etc.) and they should have someone who can tell you what you have now and what you need to change to improve the ride.