Cheap, reliable, 600HP?
Not for a long time, although it's better now.

Haven't you heard of the saying Cheap, Fast, Good; pick two.

I would start with lightening the darn car, then build a stroker 400 or 440.

BTW, why are all these posts about 500 HP lately? Sounds like a bunch of chevy bench racers reading the Car Craft covers. Before asking this, ask yourself if you have driven or ridden in a true well built 400 HP car.