I don't think a custom clutch is a bad way to go - as long as you get what you ask for. Are you running an organic or metallic disc? I don't think an organic will last very long behind a 500hp donk. They can get hammered quite quickly when slipping/dumping the clutch a little on hi-rpm launches. Also, if running a metallic disc (brass button or sintered iron) you'll need a serious flywheel and pressure plate to cope - they can act as angle grinders on normal flywheels etc.
I'm running an 11" steel billet flywheel and an 11" RAM long lever style pressure plate with a heavy duty organic disc with streetable marcel carrier (springs in hub). Total performace discs sometimes do away with the springs. They just reduce chatter on the takeup when used on the street.
I had the pressure plate resprung a few years back to keep the clamping force up, but after a little flogging and burnout session it heats up and will occasionally slip - which has me worried for my next combo with slicks. May have to upgrade to a beefier/high friction disc.
RAM lever plate on the left.