What suspension upgrades should i do for $1200 big block dart

I do have AFCO springs on my Duster, they actually come in a bunch of different spring rates. Problem is the ones that I have, the 120 lb/in version, are no longer being made. They went out of production at the same time the Mopar Oval Track springs went back into production. Not sure if that was because they anticipated a loss in sales, or because the springs are actually the same and there's a licensing thing going on. The AFCO's I use are basically the same as the oval track's, including the slightly longer front section.