Educate me on why 340 fan is not symmetrical

Blades non symeteric to prevent harmonic vibration at resonate frequency. Do you have the fan clutch for that fan? This fan was used with a fan clutch. The 213 fan did not, used on 1968 340. The issue you will have to address is the distance from fan to radiator which may require a spacer or the correct length fan clutch.