The weight of a 1988 Chevy G20 van varied significantly depending on the options and configuration (wheelbase, engine, cargo etc.). There's no single answer. You'll find a range of curb weights (weight of the vehicle without passengers or cargo) from approximately
3,500 to 4,500 pounds (1588 to 2041 kg).
To find a more precise weight for a specific 1988 Chevy G20, you would need its Vehicle Identification Number (VIN). With the VIN, you could potentially contact a Chevrolet dealership or use online VIN decoding services (though accuracy isn't guaranteed for older vehicles).