I recommend Harland Sharps as well. I know they make a pretty thick shaft, which is obviously important to minimize flex with higher spring pressures. While 500 lbs isn't a heck of a lot, it's better to have "more" than what you need as extra insurance. I've never run more than 400 lbs open, but I ran them for many years with a lot of abuse years ago in my W-2 bracket Challenger. I was glad they legalized them for IHRA and NHRA Stock. I'm near 400 but may eventually go higher. (Relatively low lift, but very long duration & steep ramps with Schubeck/Smith style flat composite hydraulic lifters.)