for the swaybar, if people are putting gen 4 bars on gen 3's, then you must be able to put a gen 3 bar on a gen4 (the boushings are a bit different though, you'll have to buy gen4 ones from whiteline)
as for the springs, i don't know, i haven't seen both side by side, but if you take a spring off the solara you shoudl be able to tell if they're the same or not