This is what I found.
THREE QUARTER TON 2WD SPECS:
Model designation:
1973-1986 Chevrolet: C20
1987-1988 Chevrolet: R20
1973-1986 GMC: C2500
1987-1988 GMC: R2500
GVW:
1973-1979: 8,200 lbs. single rear wheel
1980-1988: 8,600 lbs. single rear wheel
ONE TON 2WD SPECS:
Model designation:
1973-1986 Chevrolet: C30
1987-1988 Chevrolet: R30
1989-1991 Chevrolet: R3500
1973-1986 GMC: C3500
1987-1991 GMC: R3500
GVW:
Standard: 9,000 lbs. single rear wheel
Optional: 9,600 lbs. single rear wheel
Optional: 10,000 lbs. dual rear wheel
ONE TON 4WD SPECS:
Model designation:
1973-1986 Chevrolet: K30
1987-1988 Chevrolet: V30
1989-1991 Chevrolet: V3500
1973-1986 GMC: K3500
1987-1991 GMC: V3500
GVW:
Standard: 9,200 lbs. single rear wheel
Optional: 10,000 lbs. dual rear wheel
So if you're a dually, pretty sure is 10,000 lbs regardless of rear axle ratio
Also a pick of my fsj. Love squares n jeeps