Well a 600 watt 6 channel sounds to me like 100-200 rms. Which isn't pulling much at all. So just find a place on the chassis, sand it off and tap a bolt/nut or screw.
With that much power you don't really need to do big 3, but it's always there for future builds/upgrades.
yeah. it isnt much power. i just wanna do everything right so i dont damage my amp, and so i don't constantly have problems with it. i still wanna do the big three eventually. like you said its already done whenever i decide to upgrade, plus it'll get rid of the old dingy fades wires