304s are not made to rev real high. They make most of their torque in the lower RPM ranges unless you have swapped in a cam that likes 5,000RPM. Once you start getting up in the RPMs, the valve train is not designed for those high revs. The valves start floating first, and then you can see valve failure which can lead to the piston smacking a valve the the S hits the fan real quick.
What trans, axle gears, tires are you running?
Beat it to fit, paint it to match!
Wheel, Wrench, Repeat.