Will this radiator work as a direct bolt-in replacement?

Yes. This unit mounts at factory rocker points with no drilling or custom brackets needed. Drain the existing coolant, unbolt the old radiator, and install this one in its place.

Do I need to flush the cooling system before installing this?

Flushing before installation is a good practice to remove sediment and old coolant, but not mandatory. After installation, run the engine and bleed air from the system according to your vehicle's service manual.

Is the radiator pre-filled or does it ship empty?

It ships empty and ready for your coolant fill. Use OEM coolant type specified in your owner's manual — do not mix coolant types.