The leaf/link set-up is pretty common in lower cost S/ST & S/G cars today & many companies sell kits for it. The reason is simple--they're cheap & they work. While not a multi-adjustable 4-link system, they offer the racer some flexibility yet still retain the simplicity non-travelling racers like. I had the set-up on a 3800lb S/ST car & it would 60-foot as well as any S/G car.
Actually, if you look at a CalTracs set-up it's very similar & guys are running 8s with the set-up.
A lot of old restored S/S cars have retained this set-up & you'll see quite a few making exhibition passes with them.
As to the old, original rear suspension set-up----IIRC the cars used shocks from an Imperial as the heavier cars made for stiffer valving in the shocks & they had more travel. The rearend set-up, I'm told, was good fro about 600-650 hp before you had to supplement it. The old Lakewood 3-point rollbars were good until around 1975 or so as myself & a lot of friends had them in our 11-12 second cars. And actually you'll find pictures of Ronnie Sox running his S/S 'cuda in the early days with NO rollbar. I don't know about that, but it shows the factory gave you a bare bones racer---how you outfitted it was pretty much left to your own creativity. I know of one S/S racer that had 100lb A100 seats in his car!
