A31 AXLE CODE IN 1976 DUSTER

Hello, my name is Steve...I recently bought a 1976 Duster for a restore project....I have tried to decode the fender tag, particularly the axle code has me confused....A31 shows to be a high performance axle code....(I know probably for 69-71 vehicles) but what axle ratio is this code supposed to be for a 1976 6 cylinder 4-speed car

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