Thinking about replacing my leaf springs, and I need your advice.

If you have a 600 HP small block, they might be better on the track.
My car has a REALLY small block, only displacing 225 cubic inches. No need to worry about hooking up 600 HP to the pavement. My previous 225 Duster had 79 rear wheel HP, as actually measured on the chassis dyno. I didn't think that a chassis dyno could be calibrated to accurately measure such a low power output. My quarter mile ET at the drag strip would likely be about 23 - 25 seconds, with a trap speed of around 58 mph. And no, I'm not open to a challenge race at the strip unless its against a similarly underpowered car such as one of those awful rusty six cylinder early seventies Ford Mavericks. (Yuck.) I'd insist on lane choice, of course.