You can use the stock valvetrain up to about .530 lift. I run a .610 lift with the stock rockers but dual manley springs and titanium retainers in my LS1. I'd suggest you get a set of Comp Cams 26918-16 beehive valve springs. The CC springs are good for any cam up to .600 lift. The Thunder Racing TR224 cam is quite popular and sounds really nice.